Subject: Re: Tank Destroyers
From: johnj@wchat.on.ca (Andrew Jaremkow)
Date: Aug 15 1996
Newsgroups: sci.military.moderated

westpac7@nando.net wrote:

> Can someone tell me why tank destroyer and assault gun AFVs sometimes
> come without a movable turret? And second, with a fixed turret is the
> gun fixed, or are there a few degrees of movement around a set axis to 
> help compensate for aiming errors supplied by a driver?

	Well, here's my perception anyway...

	Why no turret? It boils down to one of two reasons, either a)
simplified production, or b) increased protection. Often the two are
combined. 
	Leaving the turret off means you don't have to build it in the first
place. This saves a significant amount of time, money, and resources.
The manufacturer doesn't have to provide the armour (thick plate is
hard to come by), a turret ring (needs good bearings), the traverse
motors/mechanism (needs good gears), the turret basket, any of the
tooling, etc. Without the weight of the turret the rest of the vehicle
can be built lighter, with less powerful engines and weaker suspension
than the heavier turreted equivalent. This allows yet another savings
in weight and resources. You could also spend the wight savings on a
larger gun than the turreted equivalent could handle. If you are in a
hurry you can slip a new gun into a preexisting chassis without the
long term investments in time and energy to field a completely new
design. (This was a major consideration in WWII Germany, where the
tank chassis designs were continually reused in various TD and Assault
gun conversions, allowing higher firepower to reach the front
quickly.)
	A turretless vehicle is also easier to protect than one with a turret.
The turretless vehicle is smaller, and thus difficult to spot and hit.
Because there is no turret the vulnerable turret ring (always a weak
spot) is no longer a problem. There is no chance that the turret will
get jammed in an awkward position. The turretless vehicle can take the
weight of armour normally put in the turret and use it to protect the
hull instead. A turretless design is usually more heavily armoured
than the tank on the same chassis. The centre of gravity of the
vehicle is also lower, improving stability (marginally) when moving on
angled terrain.

	Does the gun move? Yes, in most cases the gunner has a limited angle
of traverse and elevation within which he can aim the gun.  The
postwar JagdPanzer Kanone had 15 degrees of traverse left and right,
15 up, and 8 down. This is probably fairly typical. I can only think
of one vehicle with a completely immovable gun. This was the Strv 103,
the Swedish S-tank. It used a very complicated suspension to
accurately point the gun at the target. Coarse pointing was done with
the tracks, and final aiming was done with small actuators in the
suspension. The S-tank was a very complex machine and used the
turretless configuration purely for increased protection. It was
almost certainly the most heavily defended tank of its time when it
entered service in the mid 1960s.

	Would you believe your article hasn't made it to my end of the Usenet
yet? I found it on DejaNews. I get faster results from DejaNews than
from my server...  :(  


		Andrew "well off the superhighway roadmap" Jaremkow
		johnj@wchat.on.ca

Subject: Re: Tank Destroyers
From: "John W. Schaefer" <jschaefe@genesee.freenet.org>
Date: Aug 20 1996
Newsgroups: sci.military.moderated

In article <Dw996C.4ty@ranger.daytonoh.ncr.com>, derrick@ucsub.Colorado.EDU 

says...

>The numbers that I've seen indicate that antitank guns (towed) cost about
>1/10th as much as a tank, while a self-propelled antitank gun (tank
>destroyer) costs about 1/3rd as much as a tank.  These ratios held
>relatively constant over the period of time that Anti-tank guns were the
>anti-tank weapon par excellence.  Supposedly, ATGMs are more cost
>effective.  Interestingly, for those who consider such things; antitank
>guns were expected to destroy about 6 tanks/APCs before being knocked-out.
>This is twice what ATGMs are expected to do (about 3).  If I was an
>antitank "gunner", I'd buy the gun on my mastercard or something.

	It may be that the analysis from which those numbers were drawn 
lumped together true assault guns (the WWII Russkie 152s, for instance), the 
various AT-gun-on-a-truck/halftrack systems, and the variation-on-a-tank
designs, like the WWII German Jagdpanzer V and VI. The cost ratio for SP AT 
guns seems too low for a category dominated by the variation-on-a-tank 
designs, which are cheaper than tanks but not by a factor of 3. It would 
also be interesting to know where that analysis placed the designs that are 
visually tank-like, such as the WWII US M10, M36 and M18.

>With the new anti-HEAT stuff out there, high velocity guns may be coming
>back; especially as they could be used for direct fire support against
>other stuff.  While older antitank guns were too small in caliber to be
>particuliarly effective as HE/frag projectors, any decent AT gun is going
>to need to be 120+ mm, which translates into a pretty hefty explosive
>shell (especially if delivered with the precision necessary to hit a
>tank).

	The overriding problem with large caliber towed AT guns, even in WWII 
and much more so now, is defensive mobility. It is very easy for opposing 
artillery to take out guns that have no movement flexibility. In 1944 in 
Europe, that might have involved mortar halftracks or leapfrogging SP 105s 
providing support to armored thrusts. Nowdays, with the tremendous 
improvements in counterbattery fire management, large-caliber towed guns 
could expect to be hit from all sorts of sources.

	Modern defensive tactics also involve the ability to defend a 
strongpoint for a while, then jump to another prepared position as the enemy 
organizes sufficiently to take out your previous location. That might allow 
as few as one round from each firing point, if the assault against you is 
strong. Multi-ton towed weapons with extended and complicated movement 
processes are not survivable in that kind of fluid battlefield, because they 
have no self-defense capability once the crew commits to beginning the 
movement cycle, and even though their activity will draw attention, they 
cannot move out until the gun is closed up and hooked up, which for a large-
caliber gun can take a long time.

	That's the major advantage of fielding something like a heavy Hummer 
with ATGMs--lots of mobility. Plus they're cheap, if you don't count the
cost of training and sometimes burying the relatively unprotected guys doing 
the dirty work. Rather than bringing back 120mm++ AT guns, the various 
improvements in anti-HEAT armor are likely to lead to improvements in ATGM
warhead types, such as warheads that "fire" rod penetrators, or multi-
stage warhead systems that attack the armor first, then hit again.

                                      John Schaefer

Subject: Re: Tank Destroyers
From: johnj@wchat.on.ca (Andrew Jaremkow)
Date: Aug 26 1996
Newsgroups: sci.military.moderated

Wes Derrick <derrick@ucsub.Colorado.EDU> wrote:

>As an example; if one was to turn an M1A1 into a tank destroyer you would
>almost certainly; eliminate the heavy DU armor, eliminate Chobham armor
>(save lots of $$$), remove the turret, replace the expensive, heavy armor
>with light armor able to protect against HMG and shell fragments.

	Eeek! Remove the heavy armour?!? Sacrilege! We favour different ends
of the tank destroyer spectrum. I'd keep the heavily armoured chassis
of the Abrams, and possibly spend some of my weight dividend on
heavier armour.

>  After
>saving tons of weight by doing this, you could reduce the quality/strength
>of the drive train, use a cheaper,less powerful engine.  

	Going this far with the automotive components would mean a large
redesign and retooling and would result in what is effectively a new
chassis that shares the same shape as the M-1. I'd be more inclined to
keep the engine and drive train the same, save myself the conversion
costs, and pump out fast, nimble, rugged vehicles. There's little
point to using the M1 as a starting point if the final result is going
to have the characteristics of a Bradley.

> In short, you've
>eliminated almost all of the parts of a tank which are expensive or
>difficult to manufacture. 

	Except the electronics, which are fast becoming the most expensive
part of the tank. Two thermal imagers (on an M1A2), night driving
gear, a laser rangefinder, ballistic computer, environment sensors,
stabilization, ECM resistant radios, navigation aids, and now
datalinks and tactical computers all add up to a very significant
pricetag. If you want to add laser warning receivers, radar detectors,
and active countermeasures and jammers, well, keep shelling out.


	There seem to be two different types of tank destroyers. One is the
very heavily armoured high powered version that can take the punishing
return fire of enemy tanks, and the other is the light vehicle with a
tank killing bite, but almost no ability to withstand attack. In WWII
the Jagdtiger, Jagdpanther, and similar vehicles were on the heavy
end, while the Nashorn and M10 were on the other. Today the heavy tank
destroyer role has been largely abandoned, or ceded to the heavy MBT.
The S-tank was probably the only modern example. Light end tank
destroyers have flourished though, with platforms like the Spiral/MTLB
combination, M901, Striker, Jaguar, BRDMs, various APC/ATGM combos,
and even recoilless rifle carriers from the 60s.
	The vehicle you've described above is certainly on the light end of
the spectrum. So why start with a heavy chassis? Use a Bradley, an
LAV, or something similar. 


>  If a high
>velocity cannon can only get off one round before it must move to avoid
>destruction, ATGMs are useless.

	Eh? I believe the previous poster was talking about large towed AT
guns, which have a very large period of uselessness while the crew
frantically readies them for travel. In this vulnerable period the
missile has plenty of time to strike, and the dismounted missile crew
can be up and gone very quickly thereafter, probably beating the AT
gun out of there.

>  The higher rate of fire (and to a lesser
>extent, lack of backblast)

	Most missiles have far less backblast than a high velocity cannon of
respectable size. The muzzle blast from a 120 or 125 kicks up a very
large cloud. Something like a 140 must be truly splendid to observe,
especially close to the gound in a turretless TD mounting.

> is what contributes to the roughly 2x increase
>in kills per gun/launcher.  While this hasn't been a large enough increase
>in the past to overcome the cost efficiency of missiles, the SP AT gun is
>a more effective weapon.

	A gun armed TD is certainly far more flexible than a missile armed TD.
Its downside is that the gun is very big and very heavy if it is able
to tackle modern MBTs frontally. If you're designing a light TD I'd
stick to missiles. Only if I was making the large size and weight
commitment of a heavy TD would I go for a gun. 


				Andrew Jaremkow
				johnj@wchat.on.ca

Subject: Re: Tank Destroyers
From: "John W. Schaefer" <jschaefe@genesee.freenet.org>
Date: Aug 26 1996
Newsgroups: sci.military.moderated

Wes Derrick <derrick@ucsub.Colorado.EDU> wrote:

>>In response to an AFV-economics thread in which "John W. Schaefer" 
>><jschaefe@genesee.freenet.org> argued that turretless AFVs were
>>less costly than turreted AFVs, but not by as much as the earlier-
>>suggested 3:1 ratio:

>Why does the cost factor seem too low?  As the problem with building tanks
>was/is(?) largely a factor of manufacturing turret rings large enough to
>deal with the weight of gun/armor (...)

        Where did *that* come from? 

        Certainly if one wants high acceleration, high speed precision 
traverse such as would be necessary for a gunnery system that could track 
a target while both it and the gun platform were maneuvering on rough 
terrain at high speed, super bearings would be needed, and these are most 
practically built as freestanding cast, aged, relieved and precision ground 
tapered needle-roller assemblies with seals and integral drive-gear racks. 

        If, on the other hand, one was designing a cheap mass-produced tank 
for production in a WWII context, it would have been entirely adequate to 
mill a rectangular-cross-section bearing wheel slot track out of the hull 
itself, and use flame-carbiding to achieve acceptable localized case 
hardening. The turret would then be mounted with a suitable number of simple 
wheel modules, not unlike a pair of casters at 90 degrees to each other, 
with one wheel rolling on the flat floor of the hull track and the other wheel 
rolling on the vertical track wall, and with alignment for load sharing via 
wrenched shims. The drive rack would be machined from a casting and installed 
in sections, with inevitably imperfect but nonetheless adequate matching. 
This approach requires only a pivot-radius arm heavy miller with 360 degree 
capability and some subassembly shops elsewhere to build medium-precision 
caster/bearing modules and rack sections. If higher frictional losses in 
motion, and the use of lots of grease are acceptable, this approach to 
machine pivoting can adequately support even the heaviest static and impact-
dynamic loads, as illustrated in low-tech railroad and heavy-industrial 
equipment for decades.

>...elimination of the turret or reducing
>its weight by 1/2 by not armoring like a tank (M10,M36 &M18) should make
>them considerably cheaper. (...) Additionally, lighter vehicles (less
>armor) needed less robust suspension, drivetrain and powerplant systems.
>All of which can be translated as less expensive; often, much less
>expensive.

        The M10 and M36, I believe, used unmodified M4 family running gear. 
That was done because their engineers recognized that, contrary to your 
assertion that money can be saved by producing less robust running-gear 
components, it is almost always cheaper to use something you already have 
tooled and in production than it would be to design something similar but 
that would need new engineering, tools, testing, factory space, etc., and 
in return would save you only some steel. Steel is essentially free 
compared to almost every other cost factor in heavy machinery.

>As an example; if one was to turn an M1A1 into a tank destroyer you would
>almost certainly; eliminate the heavy DU armor, eliminate Chobham armor
>(save lots of $$$), remove the turret, replace the expensive, heavy armor
>with light armor able to protect against HMG and shell fragments. (...)

        You've just designed an AFV that is first-hit-guaranteed-killed. I 
don't know of any AFV design center that thinks it is sensible to use this
approach, either to save money or to spend the same amount of money to field 
several times as many AFVs. The professional consensus, to the contrary, is 
that the militarily proven course is to have a smaller number of MBTs that 
are extremely competent at both offense and defense.

>(...) After saving tons of weight by doing this, you could reduce the quality/
>strength of the drive train (...)

        It is common engineering knowledge that the cost of such a drive train 
is determined primarily by the number of parts, thus the size of the vehicle
and the type of mobility it is to achieve, not by the weight suspended by 
those parts. And quality is directly related to reliability, so that cannot 
be reduced.

> (...) use a cheaper,less powerful engine.

        Engine cost is determined by the complexity of the machining center 
which mills, bores and grinds the engine block, head(s), crank, etc. This is 
only slightly related to engine power. The key to engine cost is to use the 
same engine you use in many other places, so as to not have to engineer, tool 
and test and build facilities for a new design. Contrary to your assertion, 
engine power is not very strongly related to engine cost, if the comparison 
is between two engines produced in comparable numbers.

>In short, you've eliminated almost all of the parts of a tank which are 
>expensive or difficult to manufacture.

        Well, actually most elements of your analysis were wrong, but you do 
save a little money by not having to cast and machine the turret. Cost is driven
by parts count, and those are among the few parts that truly go away.  

>This of course excludes the cannon, which because of the
>massive savings in weight and such, could be up-graded to larger caliber (...)

        Gun caliber upgrades, along with some measure of cost savings from 
turret elimination, were the actual reason for the German and Russian turretless
AFVs. But the reason that gun caliber can be upgraded is not because of weight
savings, but because of the elimination of the mounting and serving limits
imposed by the front-to-back dimension that was determined by the bearing track
diameter that would fit into the hull width, because bearing tracks of course 
must be round. Without a turret, a rectangular rather than round/square space 
could be used for gun mounting and serving, so a larger and thus longer gun
will fit.

>>        The overriding problem with large caliber towed AT guns, even in
>WWII and much more so now, is defensive mobility. It is very easy for
>>opposing artillery to take out guns that have no movement flexibility. In
>>1944 in Europe, that might have involved mortar halftracks or
>>leapfrogging SP105s providing support to armored thrusts. Nowdays, with
>>the tremendous improvements in counterbattery fire management,
>>large-caliber towed guns could expect to be hit from all sorts of
>>sources.

>The problem wasn't so much that they were easily destroyed by
>counterbattery fire, but that they couldn't get to the right place at the
>right time, so that they played no role in the battle that developed.
>This very real problem is mitigated by use of SP guns.

        Yes, of course towed guns have inferior defensive mobility. You
seem to have missed reading those words in the first sentence of mine that
you quoted and were responding to. In tactical combat, it's a lot easier to
get killed being slow to get out of the position you've been firing from,
than by being slower to arrive on the expected path of the enemy thrust,
unless of course you're still arriving and positioning yourself when the
enemy tanks show up.  But that situation is not favorable for turretless
AFVs any more than it it for towed guns--defense depends on prepared
positions, and either towed or turretless-AFV guns can achieve that
condition.

>>        Modern defensive tactics also involve the ability to defend a
>>strongpoint for a while, then jump to another prepared position as the
>>enemy organizes sufficiently to take out your previous location. That
>>might allow as few as one round from each firing point, if the assault
>>against you is strong. Multi-ton towed weapons with extended and
>>complicated movement processes are not survivable in that kind of fluid
>>battlefield, because they have no self-defense capability once the crew
>>commits to beginning the movement cycle, and even though their activity
>>will draw attention, they cannot move out until the gun is closed up and
>>hooked up, which for a large-caliber gun can take a long time.

>This is true.  However, you hoist yourself on your own petard.  If a high
>velocity cannon can only get off one round before it must move to avoid
>destruction, ATGMs are useless.  The higher rate of fire (and to a lesser
>extent, lack of backblast) is what contributes to the roughly 2x increase
>in kills per gun/launcher.

        ATGMs are useless in a retreating defense? That is not an informed
comment. In a hard-pressed defensive retreat, the attacker will fire to 
suppress second rounds from any defensive position. The key to defensive 
survival, then, is to fire, then rapidly and least-visibly move to the next 
prepared position, or if desparate to the next likely cover. There is no 
reason why vehicle-mounted ATGMs cannot do this with aplomb--it is in fact 
one of their essential advantages on the modern battlefield. But towed guns 
cannot do this at all, and thus will die rapidly under such an attack.

>While this hasn't been a large enough increase
>in the past to overcome the cost efficiency of missiles, the SP AT gun is
>a more effective weapon.

        SP AT guns are more effective than towed AT guns. They're simply
different from mobile ATGMs. You're not likely to find an army that has a
defensive doctrinal leaning that will not field both, if it has enough 
money. Offensive-doctrine armies, of course, will use MBTs in place of SP 
AT guns when local defense is called for, but they will still field mobile
ATGMs.

>Additionally, whatever "fixes" can be applied to ATGM warheads can also be
>applied to AT guns.  

        Not true. High velocity guns cannot be equipped with super-diameter
warheads. Their shell weight and length is strictly limited by their firing 
dynamics and chamber lengths, so rounds containing multiple stacked, spaced 
warheads or explosive rod drivers are impossible. Also, the high velocity 
itself makes clever use of explosion dynamics much harder. All of these are 
feasible in low velocity munitions, especially if not limited by the tube 
diameter of a gun launching system.

>Expect to see large caliber tank guns firing
>self-forging warheads with terminal trajectory correction in the near
>future.

        Terminal trajectory correction of high-velocity rounds will continue 
to be difficult to engineer because of the unavoidable limitations of 
electronics in ultra-acceleration environments. (As shown in the Copperhead 
project, which had much trouble working with much-lower-velocity guns.) And 
as you go on to low-velocity rounds:

>It would further extend the lethal range of tank cannon,
>particuliarly low-pressure guns (which are easily mounted on lighter
>vehicles; if a LAV-105 works, why not a slightly heavier vehicle with a
>155 mm gun? 

        Your proposal is not quite cutting edge. The soon-to-be-removed-from-
service Sheridan, which is generally conceded to have been a failed design,
is based on a 155-mm-class low velocity gun that can also chamber ATGMs.
That proved to have been a step backward. 

                                           John Schaefer

Subject: Re: Tank Destroyers
From: "John W. Schaefer" <jschaefe@genesee.freenet.org>
Date: Sep 03 1996
Newsgroups: sci.military.moderated

An ongoing exchange between Wes Derrick <derrick@ucsub.Colorado.EDU> 
and "John W. Schaefer" <jschaefe@genesee.freenet.org>:

>Wes Derrick <derrick@ucsub.Colorado.EDU> responded:

>>>As the problem with building
>>>tanks was/is(?) largely a factor of manufacturing turret rings large
>>>enough to deal with the weight of gun/armor (...)

>>        Where did *that* come from?

>(...) my info came mostly from How to make War (3rd edition) by ???? and 
>Blitzkrieg by Len Deighton, among other sources.  (...) It has been 
>stated by many that the reason for banning armored cars with turrets 
>was to prevent the Germans from developing the ability to manufacture 
>turrets. 

        I hear your argument, but before WWII, heavy industry included 
many instances of unremarkable but perfectly adequate ring pivot 
bearings capable of static loads up to hundreds of tons and working
dynamic loads well in excess of those seen by tanks. Consider, for
instance, every heavy rotary crane in shipyard, construction and rail use.
The largest of those bearings are much larger than those needed for
tanks. Ring pivot bearings just aren't that big a deal. If you want
some aspect of tank manufacturing technology that's difficult to create,
take a look at rolling mills for alloy plate. Now *that's* a tough
bearing job, among other difficulties.

  ***************

>It was the manufacture of (turret bearing systems) which was
>believed, as I stated before, to be the limiting factor in turret size
>during the war.  Note that even the US's first attempt to mount a heavy
>gun in a tank (Grant?), mounted it in the hull.

        But not because ring pivot bearings were an unknown technology; 
rather, because the Grant's 75 was an anti-infantry artillery piece, and 
the Army didn't mount its artillery in turrets. Turrets were for anti-
tank guns. I.e., this was just another example of the influence of 
obsolete doctrine on design.

  ***************

>>>As an example; if one was to turn an M1A1 into a tank destroyer you
>>>would almost certainly; eliminate the heavy DU armor, eliminate Chobham
>>>armor (save lots of $$$), remove the turret, replace the expensive,
>>>heavy armor with light armor able to protect against HMG and shell
>>>fragments. (...)

>>        You've just designed an AFV that is first-hit-guaranteed-killed.

>As are T72s and virtually any armored vehicle that is "hit" by a top of
>the line MBT or anything designed to kill them (TOWs, etc.).

        I'm under the impression that the Russkies like to think of the 
T72 and related designs as being approximately state-of-the-art in 
defensive survivability. I don't think I'd describe their armor systems 
as being wimpy (my word, not yours, but I think a fair shorthand) like that
of the hypothetical tank destroyer being proposed.

>It should be noted that US tank destroyers during WWII were very much the 
>same.

        But surely the M10 and M36 are not to be taken as paradigms of good
design. They were notorious for their lack of defensive survivability. None
of the German SPGs that were used in what was closest to the Tank Destroyer
role in the doctrinally-more-intelligent German army were minimally
armored; in fact, all were up-armored (at least frontally) from their AFV 
versions. If somehow the U.S. had lost in Europe, or if we'd gone up against
the Russkies in 1945 and gotten our tails kicked, I'm sure the M10 and M36 
designs would have been regarded as even worse failures than the M4, because
they were so unsurvivable. They were saved from being labeled as failures
only because we were so dominant in other ways. 

  ****************

>>I don't know of any AFV design center that thinks it is sensible to use
>>this approach, either to save money or to spend the same amount of money
>>to field several times as many AFVs. The professional consensus, to the
>>contrary, is that the militarily proven course is to have a smaller
>>number of MBTs that are extremely competent at both offense and defense.

>The "professional" consensus isn't unanimous (nor is it always right).

        It is currently nearly unanimous. Whether it is right or not will be 
determined best in hindsight by analysts and historians of military 
technology, but it looked right in Desert Storm.

  ****************

>In the US, the push is towards smaller and smaller numbers of more capable
>vehicles.  However, this is probably driven as much by "we got to give our
>guys the best", as it is by any decent cost-benefit analysis.

        And that is mostly because traditional cost-benefit analysis can 
qualify, but has a lot of trouble quantifying, factors that the military is 
now expected to incorporate into its analysis. Factors such as the impacts 
on morale and Congressional/Presidential support for the military of 
ubiquitous broadcast-capable videocams and satellite video uplinks in 
suitcases; and broadcast outlets driven by competitive pressures to use 
every picture of a dead or captured GI from the conflict of the moment, and 
stick a camera lens in the face of every grieving parent and inquire as to 
whether U.S. foreign policy makes sense to them. If the political realities 
back home require that you have minimal losses, the M1Ax is a very 
intelligently designed and successful tank.

  ****************

>>>(...) After saving tons of weight by doing this, you could reduce the
>>>quality/strength of the drive train (...)

>>        It is common engineering knowledge that the cost of such a drive
>>train is determined primarily by the number of parts, thus the size of
>>the vehicle and the type of mobility it is to achieve, not by the weight
>>suspended by those parts. And quality is directly related to reliability,
>>so that cannot be reduced.

>This is not only not "common engineering knowledge", it is not even true.  

        Yes, it is true. And common engineering knowledge among automotive
engineers, AFV engineers and heavy machinery designers. 

>Do you really mean to say that a drive train which must carry 3x
>the mass doesn't require any more metal/strength etc. as long as it's
>compacted into the same size? 

        Perhaps you don't understand the design economics of the task, or 
what I wrote about it. It doesn't matter that a stronger drivetrain 
incorporates more steel. Steel is free compared to fabrication steps, 
tooling and engineering--all factors linked to parts count, not the amount 
of steel being shaped, except for secondary considerations such as 
tonnage capabilities of particular forges and dimensional capabilities of 
particular machining centers. If the vehicle gets a lot smaller, so that
the suspension has to handle a small ground contact length, it will have
fewer parts and thus lower cost. But a smaller vehicle will be limited
in mounting a big gun. If the vehicle stays the same size, it's likely 
to have an unchanged suspension cost.

>Wow!  We should just build little DU
>armored M113s, right?  Or maybe I'll use my Geo to haul gravel!?!

        Hey, go for it. My point was that within a fairly broad range, 
you can design for any strength you want, but if your parts count is the 
same, the end cost will be almost unrelated to the strength you decided 
to design for. This is a very common reality in the design of Geos and
Cadillacs, by the way...which is why GM makes so little on each Geo and
so much on each Caddy, and also why some cheap small cars seem to have 
only about 25 parts, and to be missing some of the most basic 
functionality one might expect. Cutting the parts count is the 
primary way for the engineers to cut the cost, and at some point that 
means less functionlity.

  ***************

>>> (...) use a cheaper,less powerful engine.

>>        Engine cost is determined by the complexity of the machining
>>center which mills, bores and grinds the engine block, head(s), crank,
>>etc. This is only slightly related to engine power. The key to engine
>>cost is to use the same engine you use in many other places, so as to not
>>have to engineer, tool and test and build facilities for a new design.
>>Contrary to your assertion, engine power is not very strongly related to
>>engine cost, if the comparison is between two engines produced in
>>comparable numbers.

>If the engine doesn't have to be a 1500 hp turboshaft, but could be the
>engine from a large diesel truck, it's going to be cheaper.  The very fact
>that it doesn't have to be a super-tweaked monster means that it's
>probably already being manufactured for some task less demanding than tank
>propulsion (and probably in much larger numbers).

        We agree here--if a nation has an existing heavy-industrial 1500 HP
diesel engine manufacturing capability from, say, super-heavy earthmoving
equipment manufacturing, it will have a huge advantage in manufacturing 
tanks, because it won't have to tool up a new engine. The Germans, Brits
and Americans in WWII didn't catch on to this until too late, and thus 
never had a really good engine system for either their heavy AFVs or their 
heavy industrial and construction applications. Imagine what the Panther
and KonigsTiger would have been like if a 1000 or 1500 HP automotive diesel 
and a corresponding heavy vehicle transmission had already been tooled, 
debugged and in production. For that matter, with a good 800 HP diesel tank 
engine, the Sherman would have lacked only an adequate gun system and proper
armor to turn it into a half-decent tank.

  *************

>>>In short, you've eliminated almost all of the parts of a tank which are
>>>expensive or difficult to manufacture.

>>        Well, actually most elements of your analysis were wrong, but you
>>do save a little money by not having to cast and machine the turret. Cost
>>is driven by parts count, and those are among the few parts that truly go
>>away.

>Yeah, right.  Elimination of DU armor, turret tracking and gun-laying
>system, replacement of turboshaft diesel with conventional diesel of lower
>rating, perhaps even going back a generation in chassis (M48/M60) won't
>save any money?  That's BS!  

        Like I said, cost is driven first by parts count, then by parts 
character. Elimination of the turret system saves some parts--we agree on 
that. Simplification of the armor saves some parts (and, admittedly, some 
high-quality ones)--I'll agree to that. The generation of chassis may not 
affect cost at all, if the parts count is the same--in many kinds of
machinery design, a design generation commonly increases performance without
increasing cost, and that works in reverse as well. The difference in cost 
between a turbine engine and a diesel engine is large, as one would expect 
from looking at their parts counts; there's a significant difference in 
parts character as well, of course. So sure, there would be savings in your 
example. Not all from where you proposed, but savings nonetheless.

  *************

>>>This of course excludes the cannon, which because of the
>>>massive savings in weight and such, could be up-graded to larger caliber
>>>(...)

>>        (...) the reason that gun caliber can be upgraded
>>is not because of weight savings, but because of the elimination of the
>>mounting and serving limits imposed by the front-to-back dimension that
>>was determined by the bearing track diameter that would fit into the hull
>>width, because bearing tracks of course must be round. Without a turret,
>>a rectangular rather than round/square space could be used for gun
>>mounting and serving, so a larger and thus longer gun will fit.

>Note; I said weight and such... which largely meant that the gun didn't
>have to fit in a turret.  However, perhaps you should look at the British
>Firefly (an upgunned Sherman) and think about what I've said earlier
>about weight..

        We basically agree here, but I still would note that gun weight was 
less of a limit than gun mount size and recoil mechanics in most, or perhaps 
all, WWII AFV gun upgrades.

  ************

>>>Additionally, whatever "fixes" can be applied to ATGM warheads can also
>>>be applied to AT guns.

>>        Not true. High velocity guns cannot be equipped with
>>super-diameter warheads. Their shell weight and length is strictly
>>limited by their firing dynamics and chamber lengths, so rounds
>>containing multiple stacked, spaced warheads or explosive rod drivers are
>>impossible. Also, the high velocity itself makes clever use of explosion
>>dynamics much harder. All of these are feasible in low velocity
>>munitions, especially if not limited by the tube diameter of a gun
>>launching system.

>If a 155 mm howitzer can fire all of the above munitions, tell me why a
>short barelled (155 mm snubnose?) cannot.

        I didn't make myself clear, I guess. No 6" gun, either howitzer or 
AFV mounted, can fire a (say) 12" diameter super-HEAT warhead. No 
gun with (say) an 18" max projectile length can fire a round containing a 
24" segmented rod plus a driver charge, or a stack of two 12" long HEAT 
modules. A slow shell that arrives on target at 600 m/s would require roughly 
three times the spacing between two stacked HEAT modules compared to a missle 
arriving at 200 m/s, and probably there is not enough length available in
a loadable shell for a realistic gun to allow the design. If any of the above 
features became desirable, a rail-based missle launching system would be 
easily adapted. A gun system designed into an AFV would not.

        Of course you're right that for any given gun system, progress in
munitions is possible, but it is unavoidable that a gun tube imposes real 
and significant limits on the design of anti-armor missles. The Sheridan 
experience may or may not have proved that equipping an AFV with a combo 
gun/tube missle launcher is a bad idea; perhaps a better job could have 
been done with that design with more foresight. Everyone had ideas that
would have improved the Sheridan from D- to C+ if they could have been 
incorporated, but I'm not aware that anyone ever suggested any practical 
ideas that would have turned the Sheridan into an A, because of the limits
of the gun/launcher.

>Any velocity likely to be used in a missile can certainly be duplicated with 
>a gun. 

        Yes and no. Guns fire ballistic projectiles. At 1/3 the velocity, it 
takes 3 times the peak trajectory height to achieve a hit. Having to loft all 
of your gunnery makes basic things like aiming more difficult, compared to 
nearly-line-of-sight gunnery with high-velocity guns at moderate ranges.
Missles, on the other hand, are aerodynamic, not ballistic--they can fly a
level path, or whatever path they're steered on, for as long as they have 
fuel and guidance.

  ***************

>>>(...) If a
>>>high velocity cannon can only get off one round before it must move to
>>>avoid destruction, ATGMs are useless.

>>        ATGMs are useless in a retreating defense? That is not an
>>informed comment. In a hard-pressed defensive retreat, the attacker will
>>fire to suppress second rounds from any defensive position. 

>I didn't say that ATGMs were useless in a retreating defense!  I said, IF
>you maintain that a HV cannon can only fire one round before retreating to
>avoid destruction, THEN a ATGM is useless.  Think about it, a SP AT gun
>can fire and then move, instantly.  How long does that take?  A
>wire-guided ATGM vehicle must fire and wait for its missile to go
>downrange.  If, the time required to fire an AT gun, kick the vehicle in
>reverse and run is too long, then the time required to fire a missile and
>guide it on its journey before moving is also too long (probably 2-3x
>longer).

        Noting your earlier-expressed disagreement with me as to whether 
it is safe to attribute a presumption of correctness to the consensus among 
professionals in a particular area of military technology as to the solution 
to a particular problem, I would only point out that the current consensus 
among most or all modern military forces is to include a significant presence 
of light-vehicle-mounted ATGMs in one's defensive lineup. Sure, they attract
lots of incoming when they fire. That's standard doctrine for defense
against ATGMs, to try to disrupt the aimer before impact. But they're so
cheap, small and mobile that everyone uses them anyway. AT-oriented SPGs, on 
the other hand, are not particularly common in several major armies, because 
doctrine calls for that task to be performed by MBTs.

        Part of the tradeoff is that, if the Hummer crew is still alive when
the ATGM hits or misses, they are a pretty small target with the potential
for a highly creative driving style while in transit from their firing 
position to cover or wherever. The SPG driver, no doubt, will also do his best 
Mario Andretti imitation, but the SPG can't help but be a bigger and slower 
target. Human nature being what it is, the enemy AFV gunners are likely to
want to take out big targets with their limited number of main gun rounds,
too. Thus perhaps the best possible defense for the Hummer crew is to pull 
out of position at the same moment as, and a few hundred yards to one side of, 
a friendly SPG, because the SPG will get all the main-gun attention.

                                                 John

Subject: Re: Tank Destroyers
From: "John W. Schaefer" <jschaefe@genesee.freenet.org>
Date: Sep 08 1996
Newsgroups: sci.military.moderated

M.Rapier@sheffield.ac.uk (M.Rapier) wrote:

(in response to this comment of mine, which was part of a thread in which 
I disparaged the heavy-gun, light-armor concept for AFV-like SPGs:)

>>(...) None
>>of the German SPGs that were used in what was closest to the Tank Destroyer
>>role in the doctrinally-more-intelligent German army were minimally
>>armored; in fact, all were up-armored (at least frontally) from their AFV 
>>versions.

>The Germans had two families of self propelled anti-tank weapons:
>
>1) The JadgPanzers which were generally uparmoured, turretless variants built 
>on tank chassis (Hetzer, JagdPz IV ,Ferdinand, JagdPanther, JagdTiger & the 
>Stug III with the long 75mm although this latter was strictly an assault gun).

>2) The PanzerJager which were generally lightly armoured with open topped gun 
>mountings (for better crew visibility) and which correspond much more closely 
>to the M10/M18/M36 and the M3 mounted 3" guns too.

>That the JagdPanzers became preferred later in the war is an indication that 
>the Germans recognised that their SP AT weapons needed to be more heavily 
>armoured - which is the point you are making about M36s etc.

        Yes, acknowledged. But my point in comparing to the *Tank Destroyer*
role was not to analyze *all* anti-tank SPGs, but (as I specifically
defined) to look at those weapons that were used in ways most comparable to
the AFVs of the (mis-begotten) Tank Destroyer Command; that is, AFVs that
had been up-gunned to be more effective in the anti-AFV role, then were
used essentially as general-purpose tanks.

        The Germans were able to use the Jagdpanzers with overall success as
tank substitutes. Their improved armor, lower profiles and improved weapons
more or less compensated for their decreased ability to acquire targets. 

        The AFVs of the Tank Destroyer Command were universally treated as
tanks by the infantry Army, who had no clue about AFV design and employment
doctrine but sure as hell knew that when they ran up against German panzers
or strongpoints, they needed some tanks at the point and they needed them
now.  The available TDs were not very good tanks.

        Sorry if I didn't draw clearly enough the distinction I was making 
between tank destroyers (general-purpose AFVs, upgunned to improve their 
effectiveness in the anti-armor role at the sacrifice of some capability for 
other roles) and Tank Destroyers (the infantry Army's own doctrinally-confused 
AFV force, typically employed in roles for which their designs were not 
suitable.)

                                         John Schaefer

Newsgroups: sci.military.moderated
From: "John W. Schaefer" <jschaefe@genesee.freenet.org>
Subject: Re: Tank Destroyers
Date: Sun, 8 Sep 1996 13:59:56 GMT

Steven@uunet.pipex.com (Steven Vincent) wrote:

(in response to my comment as part of a discussion of tank design
economics:)

>>        (...) if a nation has an existing heavy-industrial 1500 HP
>>diesel engine manufacturing capability from, say, super-heavy earthmoving
>>equipment manufacturing, it will have a huge advantage in manufacturing 
>>tanks, because it won't have to tool up a new engine. The Germans, Brits
>>and Americans in WWII didn't catch on to this until too late, and thus 
>>never had a really good engine system for either their heavy AFVs or their 
>>heavy industrial and construction applications. Imagine what the Panther
>>and KonigsTiger would have been like if a 1000 or 1500 HP automotive diesel 
>>and a corresponding heavy vehicle transmission had already been tooled, 
>>debugged and in production. 
>
>Sorry the British understood this very well, unfortunatly for them the
>biggest Diesel engines in use in Britain at the time were those used
>for London Busses.  These formed the bases of the Engines in the 
>Valantine and Churchill tanks.  Even so they were not really big enough
>and had to be supercharged. At the time Britain had a very developed
>Aircraft engine industry producing high performance light weight engines
>that did not have the required torque output of tank engines and a
>highly developed Steam engine industry that was used to power trains
>ships and the super heavy earthmoving equipment that you are talking
>about. Germany did have a large Diesel engine industry (hence the use
>of Diesels to power the Pocket Battleships vs the use Steam Gun Boats
>in the RN!) but their petrol engine technology was inferior so their
>aircraft performance fell behind as the war progressed while their
>Tank and truck production was well able to keep the technological
>edge.  (Even Russia had better Diesel Technology than Britain in 
>1940 and I beleive that the US was equally backward, Hence the use
>of aviation engines in the Sherman and Stuart tanks despite the
>fire hazard).

        I'm an engineer, and in my professional life, "catching onto a
problem" in time and doing something about it means not just understanding
a theoretical solution, but designing, developing, testing and debugging
parts and having them already coming off the production line and waiting 
to be installed at the point in time when you need them. No excuses.

        It is not relevant that some Brits understood in theory that their
tanks would be improved with proper engines. They didn't get it done, and
the supercharged bus engines they used were inadequate. By my standard,
the people that mattered did not "understand this very well."

        Likewise the irrelevant German large water-cooled naval diesels. 
This problem needed a super-large truck or tractor engine. None existed, 
and none was available in time. Thus they did not solve the problem, and 
the tactical employment of their Tiger II design was crippled by its 
immobility. With as much firm-ground mobility as the Panther or T-34, a 
1500 HP Tiger II would have been a truly dominant AFV on the attack--the
battlefield had never seen true heavy tanks capable of advancing faster
than opposing antitank weapons could accurately track them, and the 
corresponding shock effect would have been tremendous. But they didn't get 
it done.

        Likewise the Americans. We dropped the ball most embarrassingly of
all, because our earthmoving/civil engineering and trucking capabilities led 
the world even then, we already had enough other applications to justify
such a factory even without any demand for AFVs, and our factory/engine-line 
construction capability was superior to all other nations'. An 800 HP engine 
would have gone a long way toward making the Sherman into a good tank. We 
didn't get it done.

        For that matter, an 800 HP super-semi-truck-tractor in 1944 (akin to 
today's largest rigs, used with doubles and triples, logging rigs, etc.) 
would have taken the Red Ball Express from merely the best logistical 
operation the world had ever seen to a whole new plane of superiority, and
would have made clear a decade sooner the huge economic benefits of the
construction of a national superhighway system, thus would have brought about
a massive increase in national economic output.

                                          John Schaefer