I haven't heard of DD-M4s used in amphibeous assaults in the PTO.
I do know that M4s and M3s were used in Pacific campaigns, but they were delivered by LSTs.
On the otherhand, I do know that the Marines used AMTRACs (LVT) for beach assaults.
The DD tank was not used in the Pacific but the M4 Sherman fitted with the T6 flotation device was used at Okinawa. This was an arrangement of pontoons fitted to the front and rear of the tank so allowing it to float. Development covered in this thread
The advent of combined arms operations in World War II created the need for specialized armored vehicles. In the case of amphibious attacks, the issue arose of how best to land tanks on a beach.Although a variety of specialized landing craft were developed, the Dieppe raid in 1942 encouraged the...
I do not think that any Sherman DDs were used in the PTO (or CBI?).
M3 Lee tanks with Deep Wading Gear (ie snorkels) were used for the invasion of the Makin Atoll in 1943, and M4 Sherman tanks were used with similar Deep Wading Gear later in the war. There were Deep Wading Gear kits for the M3/M5 Stuart tanks also, and some kits were deployed to the PTO, but I do not know if any were used in operations. The tanks using Deep Wading Gear were delivered closer to shore so they could operate with the snorkels while driving on the beach bottom.
M4 Sherman tanks with pontoons (aka T-6 Flotation Device) were used to a small degree. This kit incorporated the Deep Wading Gear snorkels.
"The Ultimate Battle" by Bill Sloan briefly talks about the usage of the M4's with pontoons. Several of them went straight down into these holes near the beaching area with the crews not getting out of them. It also talked about the Marine M-4s being diesel powered which I did not know.
The A2 diesel powered Sherman was first used at Tawara and was supplied to the Marines as it was the only type that
could be spared.
It proved to be a good fit as it wasn't too big and cumbersome for beach and jungle work but it still had good armour
and gun power. HE was used most often against strong points but also against Japanese armour as most IJA tanks
were thinly armoured and AP was found to go right through whereas HE would cause major damage. AP was also
used for accurate shots into bunkers from close range to bounce around.
The A2 was supplemented by the A3 from Iwo Jima on and mostly replaced over time.
The Sherman was highly regarded by both sides in the Pacific with the tank being rated as the most important troop support
unit by the Marines and one Japanese general stating it was the difference between the two sides.