I would recomend finding a copy of the Leavenworth Papers #12 ‘US Army Tank Destroyer Doctrine in WWII’’. Copys are cheap on eBay and in the used book stores. It is a short & critical discussion of the very brief existance of the US Army Tank Destroyer Corps and its vehicals.
The M10 was the result of a pecular development in US Army doctrine for mechanized warfare. The collapse of Poland and France in the face of modern mechanized combined arms warfare used by the Germans was misinterpreted by many. There was a misunderstanding and belief with some people that the Germans had accomplished all this with tanks alone. Some senior US Army leaders became concerned with this idea. The solution selected in late 1940 was the creation of a ‘Tank Destroyer Corps’. That is specialized Tank Destroyer brigades would fight the enemy tanks.
Consequently The US Army doctrine for the new warfare was specified as: Enemy tanks would be attacked & destroyed by tank destroyer groups of 2-3 battalions. The US tanks would not fight the enemys tanks, they would be designed & organized for attacking the other enemy forces. Their infantry, artillery, supply columns.
The TD units were to be have two types of combat vehicals,: light armored cars for scouting and covering the heavier vehicals flanks, and a larger tracked vehical carrying a large caliber gun as the primary weapon. Each TD unit also was to have a small engineer section for laying & removing mines and road blocks, and a 81mm mortar section to lay hasty smoke screens, suppress enemy infantry and similar tasks.
Initially specifications for a 90mm armed TD were favored, but it soon became clear it would be 2-3 years before a suitable 90mm gun could be available. Three interm vehicals were selected, a 37mm AT gun on a light truck, a old 75mm gun mounted on a halftrack, and the M10. In November of 1942 two TD battalions armed with the 37mm gun & the 75mm halftrack were sent to Africa as part of the Torch operation. Neither weapon was very effective The Axis tanks armed with 47mm, 50mm, and a few with the new 75mm long guns could easily deal with the trucks and halftracks. Replacement M10 were rushed to Africa and these proved effective against the Italian tanks or the MKIII & MkIV the Germans used in Tunisia. In Sicilly the M10 again proved effective vs the typical German tank.
The very few Tiger tanks that were in Tunisa and Sicilly were so rare they were seldom tested against the M10, and the Panther did not appear then. So, there was little concern about more powerfull German tanks.
In 1944 in France the M10 proved barely adaquate against the latest models of the MkIV and the Panther and of course inferior to the Tiger tanks. Thus the deployment of the new 90mm gun armed M36 was accelerated.
The original doctrine for the TD brigades was abandoned. Only one such brigade was formed & it was never sent into combat. Instead the corps & divsion commanders deployed the TD battalions as antitank companys amoung the infantry regiments. The infantry comanders used them as direct fire artillery as well as AT weapons. Their AP ammo was usefull for driving the enemy out of masonry buildings and for destroying bunkers, pill boxes & other field fortifications. In those roles they were used the same as the independant tank battalions that were attached to the US infantry divsions. In effect this doubled the ‘tank’ support in the average US army infantry divsion. (Note: after July 1944 the German panzer divsions averaged about fourty to fifty tanks after losses. A US infantry divsion with its independant tank battalion and a TD battalion averaged over 100 M10 & M4 Shermans.)
Originally the open top of the TD was not seen as a problem as it was not going to go anwhere near enemy infantry, but would blast apart enemy tanks from long range.
When originally selected in early 1941 for the M10 the 3" gun was vastly superior to the standard 37mm and 50mm guns used by the German tanks of 1941. The 75mm L24 used on the MkIV in 1941 was a short low velocity designed for shootng HE ammo. The obvious problem of course is that the “interm” M10 remained in production into 1944 while the better armored M36 with the 90mm gun stagnated in development. Had the original plans worked out the TD battalions that went ashore in Normandy would have all been equipped with the M36.
Shortly after 1945 the entire TD concept & doctrine was abandoned in offcial recognition of what the combat commanders had already done. The new M26 90mm gun tank and the M46 on the drawing boards were superior general purpose tanks and filled the TD role just as well as a specialized vehical.
