From: cdm7g*REMOVETHIS*@virginia.edu (Chris Manteuffel)
Newsgroups: soc.history.war.misc
Subject: Re: "Tank Destroyer"?
Date: Fri, 13 Apr 2001 18:11:46 GMT
Organization: University of Virginia
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On 13 Apr 2001 16:11:19 GMT, chrish57@deja.com arranged electrons in
an arbitrary pattern familiar to all as:

>What is a "Tank Destroyer" please?  I was watching a show on history
>channel about the various uses Germany made of Panzer chassis
>- tanks, self-propelled artillery, anti-air, etc and they kept refering 
>to "tank destroyer" versions.
>
>They appear to be self propelled artillery (without a traversing turret) that
>fires in a flat trajectory (as opposed to the arc of a howitzer or mortar).
>
>What was the advantage of these vehicles?  Why not use a tank to kill a tank?

Nowadays they do exactly that, however, back then, things were a bit
different. There really were two different types of tank destroyers,
Western Allied and German. (The Soviets tended to use self-propelled
arty in the direct fire role for this, which is a third technique, but
not one I will be discussing.) Note that this isn't, despite its
length, comprehensive. To get the full details, read books on the
subject. I suggest books by Jentz as a good place to start. 
For the US, Britain, and France:

First, we have inter-service rivalry. Cav vs. Infantry. General Leslie
McNair, head of the US ground forces, was an infantry man, and he
wasn't going to let the Cav get all of these great new armored beasts.
So he split up the mission. 

Second, we have the issue of guns. Nowadays tank guns are optimized
for just killing other tanks, and the IFV guns are to support
infantry. But before there were IFV's the support for the infantry
came from tanks. It is difficult to make a gun that has good armor
piercing and anti-tank qualities, as they demand drastically different
muzzle velocities, calibre, etc. For example, the 16" gun on the
Iowa's, designed for piercing great thick slabs of armor, fires it
shells so fast that the "High Explosive" 16" shell has only 100 lbs of
actual explosives in the shell, the rest of the one-ton shell is metal
to make sure that the shell doesn't break up while being launched. 

Because of this problem it made sense to have one set of guns
optimized for firing high explosives, and one set of guns optimized
for killing enemy tanks. And indeed, the 76mm gun on the TD's did have
inferior HE shells compared to the 75mm's on the tanks, while the 76
had better AP performance than the 75. 

Third, armor. Doctrine called for the TD to respond to an enemy
blitzkrieg tank breakthrough. The enemy tanks would breakthrough, and
then a unit of TD's would be committed to stop them. The TD's were
fast and lightly armored. Their mission would be to quickly get to
ambush positions, and then kill a couple of enemy tanks, and then
quickly get to the next ambush position. Thus they could soak up and
delay the enemy breakthrough. Therefore, they had very thin armor and
an emphasis on speed. (Note that this was not true for the Sherman
Firefly, which use the basic Sherman hull, not the thinned down
variants used for other TD's).

The Germans had a different set of considerations for their tank
destroyers, which were very different beasts. 

The Germans needed heavier guns, and more of them, out fighting. So
they dropped the turret ring, allowing a heavier gun to be fitted,
which also had the effect of making the tank-destroyer easier to
manufacture. The Western allied TD's still had their turrets, the
Germans did not. The Germans also kept the armor that was on the hull
of the basic chassis, unlike the Western technique of lightening the
armor to make it faster. Note that the German guns were also optimized
for killing tanks, mostly, which was why they had separate assault
guns which were like German TD's but mounted a gun optimized for HE
instead of for AP. 

Chris Manteuffel 
"...the war situation has developed not necessarily
to Japan's advantage..." 
-Emperor Hirohito, August 14, 1945
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