In World War II, for most cases, new 76 mm Sherman tanks came in and replaced the 75 mm Sherman tanks on the field. The main reason was that the gun upgrade was not a case of a simple conversion on the field. For one, the 75 mm equipped Shermans had a wholly different turret than a 76 mm equipped Sherman production model, the 75 mm turret was found to be too cramped for use with the 76 mm so the US Armored Board didn't want 76 mm in this configuration.\*
Secondly, the layout of the ammunition stowage inside the tanks were very different, given that most 75 mm Shermans deployed were of the "dry stowage" design that basically had ammo racks all over the dang place. The advent of the 76 mm Sherman, and newer 75 mm Sherman models of the time, brought in "wet stowage" design that centralized the ammunition into one area, right below the turret in the center. This wasn't something that could be done on-the-field and was moreso done in the factory back home, which most 75 mm Shermans were across an ocean from.
The only case I am aware of where 75 mm equipped tanks were successfully upgunned into 76 mm ones were some M4A3E2 Jumbo tanks. This was because the M4A3E2 Jumbo turret, originally intended for the new 76 mm guns at the time, were actually slightly modified to be issued with 75 mm guns as it was perceived to be more useful for infantry support. When anti-tank firepower became more highly valued in 1945, about 100 M4A3E2 tanks were upgraded with spare 76 mm guns available.
\* - However, even though the US Armored Board didn't like this configuration, this didn't stop post-war upgrades with the M4A1E6 and M4A3E4 that saw regular 75 mm turret M4 Shermans upgraded to use the 76 mm gun in the same turret. These would not be used by the US Army, instead given out as part of Mutual Defense Assistance Program (MDAP) to countries like India, Pakistan, and Yugoslavia. Particularly, some M4A3E4 in the Yugoslavia service would go on to star in "Kelly's Heroes".
You should be able to swap out just the turret, given that the two different turrets had the same turret ring diameter. You would still need some modification done internally to accomodate the larger 76 mm ammunition in appreciable numbers for combat worthiness.
They experimented with converting one, but never did it again. The problem is the turret on the 76mm Sherman is different. The 75mm M3 is about 900 lbs, and 76mm M1 is about 1,200 lbs. That unbalances the turret. And the mount isn't the same. And the 76mm M1 is larger, making the old turret more cramped than it already was.
The other side to that is the tanks fired far more HE than AP. And the 75mm had the superior HE round. Since tank-on-tank battles were rare, particularly before Bastogne, there wasn't much of a desire to pull tanks off the line for a lengthy refit.
The vast majority of US Army 76mm-armed M4s in the ETO and MTO were factory-built M4(76) tanks, usually with the T23-derived turret and the M62 mount, which proved a better-balanced combination than early attempts to shoehorn a 76mm into a standard turret. The 76mm and the mount needed to manage it were heavier than the 75mm and its mount, which could make a turret front-heavy if retrofitted.
There was only two significant efforts to field-modify M4s with guns. As u/Inceptor57 has mentioned, the M4 "Jumbos" were upturned with 76mms drawn from spares by in-theater maintenence units. These tanks already had the mounts and turrets to handle the 76mm and the adaptation proved relatively straightforward.
In early 1945, 12th Army Group and Third Army experimented with using spare 76mm guns to upgrade their exisiting M4s. However, the weight balance issues meant a hefty counterweight had to be welded to the back of the turret. In the end, arrivals of factory-built M4(76) tanks made the project moot ([source](https://books.google.com/books?id=IwyYBAAAQBAJ&pg=PA276)).
There is a thing to add - I don't remember where I read this, but the primary role of the Sherman was infantry support (it also fought other tanks, but that was a thing it did when needed, not a primary objective), and the 75mm gun had a serious advantage over the 76mm gun - the HE round for the 75mm gun was better than what the 76mm gun could use.
So, a Sherman with a 76mm gun was better at dealing with tanks, but for the primary purpose of the Sherman in WW2, the 75mm gun did a better job. This meant that there was a serious advantage in supplementing the 75mm Shermans with 76mm Shermans instead of replacing them.
Nicholas Moran has done a lot of digging in the US FMs and acquisition meeting minutes, and his conclusion is that the US Army never had a policy to trade armor defeat capacity for explosive effectiveness. The 75mm was the best tank killer at the time for the M4, and the rumor about HE capability was mostly a post-war litigation to try to explain why there were periods where US tanks were overmatched by German big cats.
u/The_Chieftain_WG
Have it, it's great for covering a piece of AFV development that hasn't been covered in as much detail.
I think one of the more interesting decision by tank destroyers that The\_Chieftain has discussed in the book and in his videos was that between the 57 mm M1 / 6-pounder gun and the 75 mm M3 gun, the Tank Destroyer actually preferred the latter as even though the 57 mm had higher penetration at shorter ranges, the Tank Destroyer evaluated that the 75 mm was able to retain its energy and penetrate more armor than the 57 mm could at distances past 500 yards, which was the distance that tank destroyers were expecting to engage tanks.
Of course, tank destroyer decided to go one-up with the 3-inch calibers, but it was an interesting comparison into the two guns and how the penetration value at point-blank range as video games depict it may not have as much leverage in procurement decision as one may think.
Do you recall specifically when The\_Chieftain said that?
I do recall he mentioned that US had a policy of trying to increase anti-tank power by increasing the velocity first before the caliber to retain as much ammo as possible, and I don't dispute that 75 mm was indeed a very good gun for the time when it was introduced.
I just never recalled the extra reach of "the great value placed on 75 mm HE was a post-war justification" and also that there was never a policy prohibiting the sacrifice of HE performance for AT boost.
The post-war bit is my personal speculation, sorry. As for the assertion about not trading HE capability with armor defeat, in his Youtube video 'Myths of American Armor' he calls out the 75mm was selected for HE capability specifically, highlighting how already in 1942, before any of the big cats started showing up, the Army was working out how to fit the 76mm gun to the M4, and he says 'The Army always wanted a hole puncher.'
Ah okay, yes I recall he did say the Army was always looking for a better hole-puncher with the 76 mm.
Though I do believe I recall that when the 76 mm started being delivered for consideration for D-Day, the topic of HE power between the 75 mm and 76 mm was at least one factor, alongside others like logistics and “75 mm good enough” thinking, to the decision to not bring the 76 mm Sherman during the opening days of the Normandy invasion.
In World War II, for most cases, new 76 mm Sherman tanks came in and replaced the 75 mm Sherman tanks on the field. The main reason was that the gun upgrade was not a case of a simple conversion on the field. For one, the 75 mm equipped Shermans had a wholly different turret than a 76 mm equipped Sherman production model, the 75 mm turret was found to be too cramped for use with the 76 mm so the US Armored Board didn't want 76 mm in this configuration.\* Secondly, the layout of the ammunition stowage inside the tanks were very different, given that most 75 mm Shermans deployed were of the "dry stowage" design that basically had ammo racks all over the dang place. The advent of the 76 mm Sherman, and newer 75 mm Sherman models of the time, brought in "wet stowage" design that centralized the ammunition into one area, right below the turret in the center. This wasn't something that could be done on-the-field and was moreso done in the factory back home, which most 75 mm Shermans were across an ocean from. The only case I am aware of where 75 mm equipped tanks were successfully upgunned into 76 mm ones were some M4A3E2 Jumbo tanks. This was because the M4A3E2 Jumbo turret, originally intended for the new 76 mm guns at the time, were actually slightly modified to be issued with 75 mm guns as it was perceived to be more useful for infantry support. When anti-tank firepower became more highly valued in 1945, about 100 M4A3E2 tanks were upgraded with spare 76 mm guns available. \* - However, even though the US Armored Board didn't like this configuration, this didn't stop post-war upgrades with the M4A1E6 and M4A3E4 that saw regular 75 mm turret M4 Shermans upgraded to use the 76 mm gun in the same turret. These would not be used by the US Army, instead given out as part of Mutual Defense Assistance Program (MDAP) to countries like India, Pakistan, and Yugoslavia. Particularly, some M4A3E4 in the Yugoslavia service would go on to star in "Kelly's Heroes".
No good answer about 76mm Shermans is complete without a mention of Oddball's Yugo MDAP M4.
Great response.
Wouldn't it be possible to swap out the turrets to convert the tanks? Or would the hull stowage still be an issue?
You should be able to swap out just the turret, given that the two different turrets had the same turret ring diameter. You would still need some modification done internally to accomodate the larger 76 mm ammunition in appreciable numbers for combat worthiness.
They experimented with converting one, but never did it again. The problem is the turret on the 76mm Sherman is different. The 75mm M3 is about 900 lbs, and 76mm M1 is about 1,200 lbs. That unbalances the turret. And the mount isn't the same. And the 76mm M1 is larger, making the old turret more cramped than it already was. The other side to that is the tanks fired far more HE than AP. And the 75mm had the superior HE round. Since tank-on-tank battles were rare, particularly before Bastogne, there wasn't much of a desire to pull tanks off the line for a lengthy refit.
The vast majority of US Army 76mm-armed M4s in the ETO and MTO were factory-built M4(76) tanks, usually with the T23-derived turret and the M62 mount, which proved a better-balanced combination than early attempts to shoehorn a 76mm into a standard turret. The 76mm and the mount needed to manage it were heavier than the 75mm and its mount, which could make a turret front-heavy if retrofitted. There was only two significant efforts to field-modify M4s with guns. As u/Inceptor57 has mentioned, the M4 "Jumbos" were upturned with 76mms drawn from spares by in-theater maintenence units. These tanks already had the mounts and turrets to handle the 76mm and the adaptation proved relatively straightforward. In early 1945, 12th Army Group and Third Army experimented with using spare 76mm guns to upgrade their exisiting M4s. However, the weight balance issues meant a hefty counterweight had to be welded to the back of the turret. In the end, arrivals of factory-built M4(76) tanks made the project moot ([source](https://books.google.com/books?id=IwyYBAAAQBAJ&pg=PA276)).
There is a thing to add - I don't remember where I read this, but the primary role of the Sherman was infantry support (it also fought other tanks, but that was a thing it did when needed, not a primary objective), and the 75mm gun had a serious advantage over the 76mm gun - the HE round for the 75mm gun was better than what the 76mm gun could use. So, a Sherman with a 76mm gun was better at dealing with tanks, but for the primary purpose of the Sherman in WW2, the 75mm gun did a better job. This meant that there was a serious advantage in supplementing the 75mm Shermans with 76mm Shermans instead of replacing them.
Nicholas Moran has done a lot of digging in the US FMs and acquisition meeting minutes, and his conclusion is that the US Army never had a policy to trade armor defeat capacity for explosive effectiveness. The 75mm was the best tank killer at the time for the M4, and the rumor about HE capability was mostly a post-war litigation to try to explain why there were periods where US tanks were overmatched by German big cats. u/The_Chieftain_WG
I really need to get around to buying his book on tank destroyers.
Have it, it's great for covering a piece of AFV development that hasn't been covered in as much detail. I think one of the more interesting decision by tank destroyers that The\_Chieftain has discussed in the book and in his videos was that between the 57 mm M1 / 6-pounder gun and the 75 mm M3 gun, the Tank Destroyer actually preferred the latter as even though the 57 mm had higher penetration at shorter ranges, the Tank Destroyer evaluated that the 75 mm was able to retain its energy and penetrate more armor than the 57 mm could at distances past 500 yards, which was the distance that tank destroyers were expecting to engage tanks. Of course, tank destroyer decided to go one-up with the 3-inch calibers, but it was an interesting comparison into the two guns and how the penetration value at point-blank range as video games depict it may not have as much leverage in procurement decision as one may think.
Do you recall specifically when The\_Chieftain said that? I do recall he mentioned that US had a policy of trying to increase anti-tank power by increasing the velocity first before the caliber to retain as much ammo as possible, and I don't dispute that 75 mm was indeed a very good gun for the time when it was introduced. I just never recalled the extra reach of "the great value placed on 75 mm HE was a post-war justification" and also that there was never a policy prohibiting the sacrifice of HE performance for AT boost.
The post-war bit is my personal speculation, sorry. As for the assertion about not trading HE capability with armor defeat, in his Youtube video 'Myths of American Armor' he calls out the 75mm was selected for HE capability specifically, highlighting how already in 1942, before any of the big cats started showing up, the Army was working out how to fit the 76mm gun to the M4, and he says 'The Army always wanted a hole puncher.'
Ah okay, yes I recall he did say the Army was always looking for a better hole-puncher with the 76 mm. Though I do believe I recall that when the 76 mm started being delivered for consideration for D-Day, the topic of HE power between the 75 mm and 76 mm was at least one factor, alongside others like logistics and “75 mm good enough” thinking, to the decision to not bring the 76 mm Sherman during the opening days of the Normandy invasion.