A common thing I find reading about WW2 tanks is that the transition from shorter barrels to long barrels brings a pretty significant decrease in high explosive power.
When Sherman’s went from their 75mm short barrel cannon to a 76mm long barrel cannon high explosive power was down enough that the Army deliberately kept 75mm Shermans around for infantry support. Similarly, the upgrade from the short barreled 7.5cm on the Panzer IV to the long barreled 7.5cm also saw a decrease in explosive firepower. The even longer 7.5cm gun on the Panther was also criticized for not having good high explosive firepower.
Is there some reason why you can’t put your old short barreled high explosive rounds to work in your new longer barrel guns, or design a round to work in your long barreled guns that’s equivalent to the short barreled guns high explosive firepower?
Not my area of expertise, but as I understand it, if you are doing infantry support, you want a short barrelled gun for two reasons. First, you don’t get hung up on building corners and such when your infantry troops go through urban areas and you need to swing the gun around quickly. Shorter is definitely better in urban environments. Second, if you are doing infantry support you are firing at fairly close targets, and fuses aren’t instantaneous. If you use a longer barrel gun, the shell will exit the barrel at a higher velocity and may travel so quickly that it buries itself in a wall or in the ground before the fuse gets a chance to do its thing.
On the other hand, if you are doing tank-on-tank battles, the slower moving shell isn’t going to penetrate as well. So in this case you need a faster round and a longer barrel. You also need better range, which you don’t get with a slower moving shell. You don’t want to be in a place where your enemy can pound you into the dirt while they are still outside of the range of your weapons.
The Shermans had a heck of a time against German armor in WWII. This was especially true of the heavily armored Tigers. There are numerous stories of shells fired by the Shermans just bouncing off the Tiger’s thick armor. In contrast, the Tiger could easily put a shell in through the front and out through the back of the Sherman. The bigger and longer-barrelled gun on the later Shermans wasn’t as good for infantry support, but it gave the Shermans a better chance against German heavy armor.
This is true. The M48 HE shell used in the 75mm tank gun weighed 14.7# with an explosive weight of 1.47#. The M42A1 shell used in the 76mm tank gun weighed only 12.87# with explosive weight of 0.86#.
This is doubtful. Production shifted over entirely to 76mm M4’s during 1944. There were just never enough of them produced to entirely replace 75mm gunned vehicles, during WWII. In the Korean War while the US tank force was a mix of M26 and M46 90mm gun tanks as well as M4’s, all the ‘regular’ M4’s were 76mm. In both wars there was a turreted 105mm howitzer version of the M4 (as opposed to the M7 105mm ‘Gun Motor Carriage’ self propelled arty piece) specifically for direct fire support, though a shortage of them in WWII meant M7’s were sometimes substituted for them in tank battalion assault gun platoons.
This isn’t true. The explosive charge volume of the Sprenggranate 34 and 42 was similar, the weight and power varied slightly depending on the charge material but was a little more in the later not earlier rounds. Both were roughly comparable to the US 75mm tank gun HE round. The two rounds in various versions were used across the ‘short’ L/24 in early Pzkfw IV and various ‘long’ 75’s (L/43, L/48, L/70) in later IV’s and the Panther.
I have seen this contention elsewhere on web but seems it might be an artifact of computer games, which in turn might be a function of varying WWII references (one US evaluation of captured Spgr. 34 said it had a 1# charge but that’s apparently incorrect). Or perhaps it’s via the observation that the Panther fired a smaller HE round, since it had a smaller caliber gun, than its eventual rival the T-34-85.
The point brought about (un)handiness of the turret on some later German tanks is true but seems a slightly different point. It seemed most critical in tank v tank battles in close terrain, as in the anecdote in ‘Is Paris Burning?’ of an M4 saved from a shot by a Panther because the Panther’s gun barrel hit a lamp post before it could be brought to bear. Also when its engine was running at low rpm the Panther’s turret traversed significantly more slowly than the M4’s, and late Pz. IV (ausf J’s) eliminated power traverse. But in a lot of cases tanks didn’t have to traverse their turrets rapidly or even much.
I posed this question to a friend of mine, who is a tank warfare expert, with several books published on the topic.
He said that the rounds were designed for different purposes - infantry support for the 75mm and anti-armor for the 76mm.
Presumably, when your purpose is to punch a hole in an enemies’ tank, the shells are designed with more metal to increase their penetration, reducing the explosive load. But, that’s not a big deal, since once your shell is inside the tank, the crew is going to be toast just from the metal shrapnel bouncing around.
So, why was that?
From wikipedia, it appears that the lack of effective HE was a complaint about the 76mm at the time, so I don’t think it was just a design decision that 0.8 # was enough HE to do the job. Was it just the geometry of the 76mm that prevented a larger shell?
That doesn’t make much sense. Both the 75mm and 76mm had separate Armor Piercing shells and High Explosive shells, and tanks (no matter which gun they had) carried both kinds, shooting AP at armor and HE at infantry. There’s no reason to intentionally make the HE worse at killing infantry as they’re never going to be able to punch through a tank’s armor anyway.
The M48 75mm and M42A1 76mm rounds mentioned above were both HE. Neither was intended for penetrating significant armor. Each of the guns also had AP rounds. The common conventional armor piercing rounds were APC M61 and APC M62A1 respectively*. Those had the same (much smaller) explosive weight: 0.144#. The M62A1 from 76mm could officially penetrate 3.5" of homogeneous armor at 1000 yds 30 deg angle v 2.4" for M61 from 75 basically from higher muzzle velocity, otherwise similar shells.
The difference in the two HE rounds was based on different origins though. The M48 was the HE round of pre/early war 75mm field artillery pieces such as the M1897 (‘French 75’). The M42A1 was the HE round for pre/early war 3" antiaircraft guns. The ‘76mm’ was the same caliber as the 3" AA gun (and the AT guns directly adapted from it) but with a smaller cartridge case. Probably the difference in explosive wt % (10% for M48, 6.7% for M42A1) was based on more emphasis on fragmentation and less on blast in an AA shell. It was also just smaller/lighter, to loft it higher in its original role.
*eventually the 76mm also had a Hyper Velocity Armor Piercing round, a still lighter (9.4#) non-explosive shell with a tungsten core and light alloy body, the cousin of discarding sabot rounds except the light body didn’t break away but stayed on the core till stripped away when it hit the target. Those were scarce in the closing months of WWII but a standard item for M4’s in Korea. Official penetration capability v RHA at 1000 yds 30 deg angle was 5.3".
It appears that the poor HE load was seen as a drawback at the time:
I wonder why they didn’t develop a new HE shell for the gun, particularly since the existing AA shell needed a new cartridge case anyway, so there’s not that much logistical saving from keeping the low-HE ammo.
Yes, in fact the drawback was if anything highlighted more before the gun actually entered service. After large scale commitment of the Army in NW Europe in summer 1944, it was apparent even the 76mm wasn’t enough of a hole puncher v German tanks and any actual preference for the 75 fell way.
A lot of US weapons decisions in WWII can be second guessed but the reasoning usually included a very heavy emphasis on going with what was available right then and minimizing production delays. In that vein they might have just fitted a direct AT gun adaptation of the 3" AA, as was carried by M10 Tank Destroyers (which were basically the same as M4 tanks mechanically). And the again similar M36 TD carried a 90mm, heck eventually the Israeli’s fitted 105mm long guns to M4’s. So even taking the time to develop a lighter 3" (the ‘76mm’ with smaller chamber volume) for tanks could be viewed as unnecessary in retrospect. But not stopping to design a new 3" HE shell was in keeping with the general approach of the time. And in the big picture it wasn’t that big a deal. Although to be fair the low performance of US tanks v German in 1944-45 though more important wasn’t as big a deal as it’s sometimes made out to be. The US doctrine held that tanks’ main mission wasn’t to combat other tanks, and it usually wasn’t in reality. It was often enough however to create a problem when over matched as seriously as 75mm (particularly) M4’s were v Panthers, Tigers and various heavy assault guns.
The 76mm (and the British 17pdr) HE shells were thicker walled to resist the significantly higher propulsive forces without damage. This left less room for explosive filling, so lesser performance against non-tank targets. The even further reduced 0.144 lb explosive filling of the 76mm M62A1 APC round was not significant for anti-tank use (and the alternative M79 AP and T4 (M93) HVAP (APCR) rounds were solid, with no explosive filling).
Note that the standard British TOE called for a mix of 2 17pdr “Firefly” and 2 regular 75mm Shermans per troop, to retain the greater HE capability against infantry and anti-tank guns while still having an effective weapon against the later German tanks. The regular 75mm was still good enough for the Panzer IIIs and IVs that made up the majority of German tanks, and could also penetrate the thinner side armour of the Panther.
Firstly, shermans did not encounter tigers on any regular basis.
Most tiger I tanks were used and lost on the russian front.
The Tiger I has 100mm of frontal armor, 80mm on the sponsons, 60mm on the lower sides, and 120mm on the mantlet, 82mm on the turret sides and rear.
The tiger is also made of FHA
Non penetrating rounds do one of 2 things.
Shatter on the face hardening if they are smaller rounds, or embed if they can break through the face hardening but not fully penetrate.
The 75mm sherman could not penetrate the tiger I frontally at all, and flanking only from within around 100m.
That is not very good, but again the 75mm shermans saw very few tiger engagements, and if they did run across one directly engaging it would not be the 1st course of action.
The extreme rare occurrence of dealing with a Tiger I is one of the reasons the US did not upgun the sherman until 1944.
Also, while the Kwk 88 can penetrate the sherman, it does not shoot through the front and out the back, it does not have that much power, nor do Tiger I’s enter tank engagements in close range, they are standoff weapons preferring to engage targets
somewhere in the 1500 to 2000m range where their mobility and turret traverse do not put them at a disadvantage.
It can penetrate most of the sherman’s armor out to 2000m, but not the upper glacis, even close up.
The 76.2mm gunned sherman though is a different animal entirely.
Firing M62, It can penetrate the Tiger I’s flanks with out too much difficulty from any practical range, and it could penetrate the Tiger I frontally nearing 2000m in range.
The same round in the M5 cannon of the M10/M18 tank destroyers does even more damage.
But there would be few of those engagements happen again because most of the Tiger I’s were expended on the eastern front, and there were never very many tigers
to begin with.
The tiger II would be a different story, but only a few hundred of those would ever exist.