So, what's your take on this? Was the 76 really an upgrade overall? Sure, it had somewhat better penetration, but the 75 had a better HE round and WP rounds.

The 75mm had zero chance of getting through the front of a Panther, which was fast becoming the standard German medium.

The 76mm at least had a reasonable chance of getting through the turret front at ranges inside 500 metres. Its HE round wasn't quite as good but was still perfectly good enough.

All in all I think its a no brainer....the 75mm should have been upgraded some time earlier and, frankly, to a better gun than the 76mm.

I think the Brits had a good idea with the mixed platoons....1-2 with the 17 pdr and the rest with the 75mm.

The 75mm M3 was a tank gun. Tanks in order to perform their job require a gun that can both knock out the majority of enemy tanks at normal combat ranges but also have significant general purpose capability. As much as many people like to think that tanks spend all their time hunting other tanks and exist for that purpose the truth is rather different. A huge number of tankers, particularly American tankers NEVER fired on a German tank, let alone a Panther. HE and WP ammunition expenditure far exceeded that of AP.

The 76mm was an anti-tank gun, concieved with the primary purpose of arming tank destroyers (like the M18) to go after enemy tanks. While it could fire HE the 76mm guns HE shell had something like half the explosive capacity of the 75mm. Thus it is no surprise there was little enthusiasm for mounting this gun in tanks. As I recall by July 1944 the plan was to produce one 76mm gunned M4 for every four 105mm gunned M4's and discontinue the 75mm model altogether. The appearance in numbers of German armored vehicles with significant armor (not just the Panther and Tiger but the Jadgpanzer IV and Hetzer too) caused enough concern that 76mm armed Sherman's had to be increased.

Fact of the matter is, the United States, in the understandable desire to speed production so as to properly equip the rapidly expanding armed forces did not foresee how the needs of armored warfare would change. What was adequate in the summer of 1942 wasn't likely to be adequate in the summer of 1944, but nothing was done about it because up until April of 1944 the M4 had proven totally adequate. In hindsight, neither the 75mm, 76mm or 105mm was really going to the answer. By July 1944 the 76mm gun was simply too little too late as it was not wholly adequate against the new German armor anyway. A completely new gun should have been considered and that gun did exist. It was even technically feasible to mount that gun on the M4 and have it ready in time for the invasion of Europe. But because the 3 or 4 agencies responsible for decisions on tank production couldn't agree, the 90mm was held back.

Panthers were very vulnerable on its left and right flanks, m1 57mm anti tank guns (U.S equivalent of the U.K 6 pounder) easily knocked panthers out in the early days of Op.Cobra.
The 76mm sherman had a better AP round, but a less powerful HE round, so they mixed them together. I dont really think the panther was the standard late war medium, i would think Panzer IV's as the main medium tanks

After the first encounters with the Panthers the US tankers wanted as many 76's as they could get. There was even better ammo available from the TD's. So from the soldiers point of view, the 76's were better. And, if the idiots had not decided to down grade the gun by wacking off a couple feet!?!?

Imagine the result if the procurement offices were not so heavily staffed with artillery officers. These men considered tanks toys, and the "big guns" the rulers of the battle fields. Their pets were the TD's, and they went to a lot of trouble to make sure their pets did not have any competition. Remove that short sighted view and a new tank similar to the Tiger might have been available in Normandy. Or, we could have been mass producing a 17pdr in a properly designed turret.

I did say it was "fast becoming" the standard medium...in the second half of 44 and in 45 you would find that there were as many Panthers as PIVs in the Panzer Divisions if not more....not to mention the JpzIVs, JadgPanthers, Tigers, Hetzers and others, all of which were invulnerable to the 75mm from the front....

BTW random fact for the day...the US M1 57mm ATG wasn't just the equivalent of the 6pdr...it was in fact the 6pounder, manufactured under licence. Once the US got to Tunisia and realised their 37mm was useless and the 76mm a bit unweildy for the infantry battalions, they needed a quick fix and the 6 pounder was it.

I don't think that is true at all. Tanks were considered exploitation vehicles, not tank-killers and certainly not "toys". The 75mm was still an excellent TANK gun under that doctrine. It just couldnn't kill Panther's frontally. But how many M4 gunners ever even had a Panther in their sights? I guarantee it is a small minority. Remember too, even the 3" guns used by the tank destroyer battalions proved absolutely inadequate against the Panther in they July fighting. The 76mm gun, with essentially the same AP performance and inferior GP capability was not really an answer.

There was a failure to foresee future requirements across the board. The M4 for example was designed to a 1941 requirement which recognized the 3.7cm PAK36 as the standard infantry anti-tank gun, thus the M4 had armor to protect against this threat. Nobody seems to have given much though to what anti-tank guns would be in 1943-44. Just as development of the M4 started the same day the M3 was ordered into production, so to IMHO should plans for an M4 successor begun in earnest far earlier. 1945 was too late. The tank destroyer doctrine had proven faulty already by the end of 1942. If the lessons had really been absorbed perhaps the TD battalions could have been eliminated as they should have been and that effort devoted to an earlier M4 replacement. At the very least TD's should have had 90mm guns from 1943 but that was another failure to foresee requirements.

In a really ideal world the T25 with a 90mm gun would have replaced the M4 in production by the spring of 1944 (if not earlier) and TD battalions would have been reorganized as tank battalions and assigned directly to infantry divisions. But then, this would have totally upset the invasion plans. The 76mm wasn't really an answer because it reduced the tanks ability to do its primary job. The 17-pounder was certainly NOT the way to go as it was even worse in that regard. It didn't even have a HE round until the fall of 1944 and tanks fire far more HE than they do AP rounds against tanks. The 90mm gun resolves all the firepower issues and using the T25 keeps it packaged in a tank that maintains the M4's advantages of strategic transportability and tactical mobility. The T26 I think was a mistake. The extra armor was not enough to grant it significantly more immunity from German anti-tank weapons while the extra weight was a significant handicap. It didn't become viable until more powerful engines were available post-war.

If nothing else, the German's had a HEAT round for the 7.5cm PAK 97/38 which had proven far more effective than conventional AP rounds against tanks. Had the American's copied this ammunition and had it available in quantity by the invasion of Europe it perhaps could have at least eased the strain. I am not proposing it as "the solution" naturally, because that would have required a new tank and gun.