On the surface they look similar. However, obviously they are not. So, what’s the difference?
tank destroyer, a highly mobile lightly armoured tank-type vehicle that was used to fight tanks in World War II. Tank destroyers tended to have relatively thin side and rear armour, and the gun was mounted in an open turret or in a casemate that had only a limited traverse. This made tank destroyers lighter, faster, and easier to manufacture, but it also rendered them more vulnerable to enemy fire. They compensated for this with thick frontal armour and a large long-barreled high-velocity gun that was capable of outranging enemy tanks.
So, a sniper tank.
My uncle was in a tank destroyer and landed on D-Day plus three. He told me that the main battle plan was for three souped up, lightly armored vehicles the size of a Ford F450 to harass a German tank with heavy guns while one came up behind them and torched them with a gun mounted flamethrower.
He obviously developed big balls due to having survied experiance.
Its a doctrinal, basically philosophical, thing. The official policy of the US army to counter the panzers was “Tank Destroyer doctrine”, where it wasn’t the job of tanks to attack other tanks, that was the job of “tank destroyers” (which did end up looking a lot like tanks, as the OP says, but no don’t call them that, they are tank destroyers!). A detailed description is here (which is a somewhat revisionist take, saying the idea wasn’t so bad, that personally I"m skeptical of):
So half the vehicle horsepower was dedicated to hauling the crew’s balls around.
Yeah, my understanding is that a “tank destroyer” is basically a big tank-killing gun mounted on relatively cheap chassis compared to a main battle tank. Unlike the tank which is an all-purpose weapons platform for assault, defense, maneuver, and infantry support, the tank destroyer is just designed to roll into position and shoot tanks and other armored vehicles with direct fire from it’s main gun.
There is also the “self propelled gun”, which also looks like a tank, but functions as long range artillery lobbing indirect fire from great distances.
The Wehrmacht had similar equipment and doctrine, although I don’t think they were doctrinally opposed to tank-on-tank engagement.
So the critical difference is the Germans (and everyone else in the war) thought of tank destroyers as mainly defensive weapons. So they had turretless, well armored things like the Jagdpanzer and the Stug (these proved to be the most effective armored vehicles in the wermacht*). American tank destroyer doctrine called for tank destroyers to actively hunt down enemy armor, hence they had turrets and looked like tanks.
* - the Stug in particular was one of the few examples of Germany “cutting its clothes to match its cloth” and was a simple effective (originally Czech) design not overly complicated in a way that would burden the limited resources they had.
Originally tank destroyer doctrine started as a response to the German Blitzkrieg, as a way counteract a tank breakthrough. The US used both towed anti-tank guns and tank destroyers in tank destroyer units. The idea was a fast, lightly armored vehicle with a powerful anti-tank gun that could stop a breakthrough and knock out and ambush tanks, using its speed. The M10 and M36 Tank destroyers were based on the Sherman tank chassis, so reasonably mobile. The M36 especially was valued as it carried a 90mm gun, appearing late in the war.
The M18 Hellcat was extremely fast, and was the ideal tank destroyer per doctrine, but the 76.2 mm gun had trouble with the Panther and Tiger tanks.
It turned out most tank destroyers ended up being used as tanks, lobbing high explosive shells more than fighting enemy tanks. The stock Sherman 75mm gun had a much better HE round, though the armor piercing capability was lacking.
The tank destroyer doctrine was abandoned after the war.
Sort of… the Germans and Russians weren’t doctrinally opposed at all to tank v. tank combat, but both were put in positions where they were facing enemy tanks with more powerful armor than their tanks of the day could readily penetrate. So they made vehicles armed with more powerful guns to take them out, even if they were often conversions of obsolete tanks with casemate/lightly armored open emplacements. The Panzerjager 1 is an example- they took a PzII chassis, and mounted a 47mm anti-tank gun in a lightly armored open mount. It was reasonably fast and powerful, but not well armored.
Both the Germans and Soviets tended to adapt their infantry support “assault guns” to be effective in the tank destroyer role- the German Stug-III and Soviet SU-series are examples.
As the war progressed, it became apparent that for ambushing tanks, the turretless assault guns were very effective, as they had a very low profile and were very concealable. So the Germans continued with the low profile casemate tank destroyers like the Panzerjager 38t (Hetzer), the Panzerjager IV, Jagdpanther, and upgunned Stug-IIIs.
The British armored doctrine was frankly a mess during the first 2/3 of the war, and they ended up doing things like making the Archer, which was a Valentine chassis with a 17 pounder antitank gun mounted on it (in reverse!). Fairly early on they started using American M10 tank destroyers, both with the stock 3" gun, and with the 17 pounder gun (the “Achilles”).
American doctrine was the most interesting- we specifically had the doctrine that tanks were for infantry support and exploiting breakthroughs, and that tanks were specifically to be engaged by tank destroyer units equipped with lightly armored, fast, and heavily armed (i.e. powerful gun) vehicles. Problem was, we didn’t really achieve that in practice- the M10 and M36 were reasonably mobile, but not fast, and the M10 wasn’t even particularly powerful. The M18 Hellcat was close to the platonic ideal of the American tank destroyer however. (See @gnarator’s excellent description of the doctrine above; I was ninjaed while writing the post)
Eventually everyone involved realized that tanks were the best thing to fight other tanks with, so they eventually fielded tanks to fight other tanks like the M4A3 (76), which was a M4 Sherman with a 76mm high velocity gun, the Comet, the T-34/85, and the Panther. The thing was that the Germans figured it out in 1941 , and were fielding the PzIVF2 by March 1942. The Russians apparently had figured it out pre-war, and were already fielding the T-34/76 and the KV-1 when the war started.
Tank destroyers were kind of a product of their time in a lot of ways, but today what tends to fill the role are IFVs and other light vehicles with ATGMs, as they are fast, can get in position, and can hit the enemy hard from long range. In a lot of ways, they are closer to the platonic ideal of the light, fast, hard-hitting tank destroyer than anything else, and it’s all because ATGM launchers are lightweight and small relative to a gun of similar capability.
The upshot of the Army doing this dual armored vehicle doctrine is that the hugely superior Pershing tank arrived in Europe just a few months before the German surrender. Blame mainly fell on general Lesley McNair and his abject refusal to ok full scale Pershing production.
Not to be confused with Panzerjäger. Or to be confused with it, one way or the other. Panzerjager were generally open-topped, thinly armored conversions of older chassis with larger guns than could be mounted on the original, turreted vehicle. Jagdpanzer were generally fully enclosed and more or less well armored. StuGs were strictly speaking not tank destroyers at all, the word Sturmgeschütz means assault gun, they were initially armed with the same short-barreled 75mm gun for infantry support that the early Pz-IVs used before later models of both were equipped with the longer barreled 75mm making them effective tank-killers.
A few things to note, WWII US turreted tank destroyers were all open topped which exposed the crew to the elements as well as artillery fire. A big reason for Germany’s reliance on turretless assault guns/tank destroyers is that 1) a larger gun and better armor protection could be fitted on the same chassis if you do away with the turret and 2) doing away with the turret makes them much easier and cheaper to produce.
Finally, regardless of what official doctrine on them was, the realities of the battlefield forced vehicles to perform anti-tank and infantry support duty, whether that was what they were ‘supposed’ to do or not. A US infantry division in Europe in WWII would generally have an independent tank battalion and an independent tank destroyer battalion more or less permanently attached to it. The tank destroyers wouldn’t sit around doing nothing if there were no hostile tanks present. Particularly so for tank destroyer battalions sent to the Pacific theater, where there generally weren’t very many Japanese tanks to fight.
Good and interesting posts, you and all.
How similar or different are these rounds and their guns?
The US 3" gun was based an anti-aircraft gun. It had decent armor penetration, but was an older design. The English 17 pounder was also a 3" (76.2mm) round, but it had a much larger propellant charge inside a heavier case–it was the best allied anti-tank gun of WWII.
The English were able to fit 17 pounders in Shermans by changing the gun design somewhat and modifying the turret, to create the Sherman Firefly.
The 3-inch was the 3-inch gun M1918 with a barrel length of 40 calibers, the 17 pounder was the Ordnance QF (Quick-Firing) 17-pounder with a barrel length of 55 calibers. The 17 pounder was an extremely effective anti-tank gun compared to the 3", or pretty much any tank/anti-tank gun used by the Western Allies. It fired either APC or APCBC (Armor Piercing Capped or Armor Piercing Capped, Ballistic Capped) as its basic anti-tank round, capable of penetrating 163 mm of armour at 500 metres and 150 mm at 1000 m. APDS (Armor Piercing Discarding Sabot) rounds for it started entering service shortly after the Normandy landings, which allowed it to penetrate 256 mm of armour at 500 m and 233 mm at 1000 m.
In other words, the 17 pounder was capable of frontally penetrating the armor of the heaviest of German tanks that were causing nightmares to Shermans armed with the 75mm or even the 76mm gun.
I tried to find pictures comparing the rounds, and was not completely successful.
Here are US antitank rounds:
1 and 2 are 37mm, 3 and 4 are 57mm (6 pounder), 5,6,and 7 are the 75mm as found in the Sherman, 8 is the 76mm from the Hellcat and the Sherman 76, 9 and 10 are from the 3" M1918 in the M10, and 11 is the 90mm from the M36 Jackson and the Pershing.
British antitank rounds:
(from left) 2 pounder, 6 pounder with special APDS round, 75mm as found in Sherman, 17 pounder with APDS round, 77mm from Comet tank, and the last two I don’t know. You can compare the case sizes and get an idea of the power of the respective rounds–sort of like comparing a 30-30 to a 30-06–same caliber, but quite different rounds.
76.2-mm howitzer explosive (Churchill), 95-mm howitzer explosive (Cromwell, Churchill)
This according to a random site I found, but they match all the ones you listed as well.
Adding to this informative post, the three tank destroyer battalions that saw combat in the Philippines (where the Japanese employed tanks) operated almost exclusively as assult guns and supporting artillery.
There was talk about using tank destroyers in the planned invasion of Japan for attacking Japanese-style fortifications.
Also note that these tank destroyer battalions were part of the US Army and the Marines did not use tank destroyers. The Marines did not have their own tanks, but rather depended on being supplied by tanks from the Army.
Tank destroyers were not deployed in the Central Pacific island hopping campaign by the Marines, but were used by the Army in New Guinea and the Philippines, as well as some limited action in Okinawa.
I was a bit confused by the way this was worded at first, but digging around a bit I’m pretty sure I get what you mean, but just to clarify that I’m understanding you correctly: the Marines had their own tank units manned with Marine personnel, but the tanks themselves to form such units were acquired from the Army. I wasn’t aware that the Marines acquired their initial (or all?) physical tanks themselves through the Army, but all six Marine divisions raised during the war had their own organic tank battalion as part of their divisional structure, unlike the US Army, where tank battalions operating with infantry divisions were independent units, but as noted each infantry division had one more or less permanently attached.
The U.S. Marine Corps’ Tank Doctrine, 1920–50 (usmcu.edu)
Marine Corps decisions such as forming an organic tank battalion in each Marine Corps division, fielding unarmored amphibious tractor (amtrac) battalions for resupply of landing beaches, and adding an antitank battery of M3 75mm guns mounted on halftrack vehicles to each divisional special weapons battalion reflected no Army influence, concept, or doctrine. The Marine Corps Quartermasters viewed Army weapons developments with varied interest, but no transfer of doctrine took place when “Army technology [was] purchased by the Marine Corps Equipment Board in 1938 [sic],” as DiDomenico incorrectly wrote. He later clarified this statement: “In 1938, the Marine Corps Equipment Board met to discuss the future of Marine tanks. They concluded that the Marine Corps would purchase some tanks from the Army’s arsenal of M2A4 light tanks and test their abilities during FLEX 6 in January 1940.”18 However, as previously noted, the actual Navy request for 36 Army light tanks wasn’t made until 8 July 1940. U.S. Army infantry divisions had no organic tank battalions in World War II, using instead a pool of field Army level tank battalions as required.