For the most part it depends on a couple of things. Firstly what branch is the tank in? Marine or Army. This is because the US Army was not just fighting on one front, but three, Italy, Pacific and western front. And the US army had to plan accordingly to combat opponents in all 3 settings, this included the mountain climates of Italy, the fields of western France and the tropical beaches of the pacific. This is why Army Divisions are set up the way they are, pretty standard and general across the board. Each division is given a service company, medical, tank ect.

It’s because of this set up that Army units in the pacific were given all the same types of ammunition as the ones in the ETO. The army divisions in the pacific such as the 7th, 27th 77th, 96th infantry all had tank destroyers too, along with Shermans. So we can assume based off of logistical evidence that tankers were given these other kinds of rounds. That and depending where they were, they may switch up the round, such as at Okinawa where defense in depth and cave warfare was encountered for the first time by a corps sized army unit.

What about the Marines? Well they’re very different than the army because the marines only had one opponent in the war, the Japanese. The marines thus could change their divisions around to combat the Japanese better, this is why Marine divisions featured “assault platoons” which were platoons who operated from battalion level and were given sub machine guns, carbines and rockets. The reason being the marines preferred aggressive close range infantry attacks over the typical army French 1918 battle doctrine, of shelling the opponent then attacking. It’s because of this reason Marine tanks may of had the option to decide what kind of ammo they wanted, and I’m sure since the 1st Marine division and then others in the 3rd, 4th, 5th and 6th encountered Japanese cave warfare for the first time, they too took APHE among normal HE.

So we can safety say that it’s a rumor. Tankers were given ammo from ordinance, that is Marine and Army units as a whole. This rumor may come up from tankers only deciding to use one round over another, probably HE to combat cave warfare, but I can’t be certain. I tried finding out more by looking some of the larger tank engagements of Shermans, such as Kakazu ridge, Conical hill and sugar loaf ridge from Okinawa as that’s the battle I’m more familiar with and it seems that they fired both kinds of ammo depending on what they were shooting at but leaned towards HE, perhaps to blast caves closed as that’s what they found themselves doing in a large part of the battle of Okinawa.

Hope this clarifies, it’s actually a hard question to answer but I’m definitely willing to do a follow up if you have any more questions.

The Japanese armour that US tanks faced was feeble. The main Japanese tank, the Type 95 Ha-Go, had 12mm armour, while its heavier stablemate, the Type 97 Chi-Ha (classified as a medium tank despite weighing only 15 tons) had 15-25mm of armour. The 37mm gun (M3) was sufficient to defeat the armour of these tanks - a convenience for the Marines, since it was compact and mobile, and could be manhandled on the battlefield far more easily than the AT guns that were needed in Europe to face tougher enemy tanks. The M3 Lee, carrying the M3 gun in its turret as its main AT weapon, was more than sufficient to defeat Japanese tanks, and served with success in the Pacific theatre long after it was obsolete in Europe.

As for the M4 Sherman with its 75mm M3 gun, its solid AT shot, the M72, would go completely through the Type 95 or Type 97 tank at a distance of a kilometre, leaving a neat hole through the tank, often without knocking it out. The M61 AP-HE shot had an explosive charge that would explode after penetration, but this shot (which replaced the M72) had even better penetration, and could go straight through a Japanese tank at ranges as great as 3km, again leaving a neat hole through the tank. Against such thin armour, general-purpose HE shells proved better, as they would easily defeat the armour, and reliably damage the interior. The Japanese tanks were too lightly armoured for AT ammunition to be the effective choice.

The Japanese army realised the inadequacy of its tanks, and developed better armoured tanks: the Type 3 Chi-Nu with up to 50mm of armour, and the Type 4 Chi-To with up to 75mm of armour. However, the few tanks of these types that were made were kept in Japan to face the expected US/Allied invasion. These types did not see combat, and Shermans firing HE shells were overwhelmingly superior to their lightweight opponents in battle.