It has crossed my mind a few times now, and i thought to seek the knowledge of an historian. Also i thought it to be an interesting discussion.
For one, i find it quiet odd. Since it was used to quite an degree in the Pacific theater, judging by the success it had on a lot of the beach landings on island's. I don't see why they didn't use them during the D-day, seeing how they could also be equip with a 37mm and 75mm gun.
At the time, there was not enough LVTs for use in both the European and Pacific theaters. The initial stages of Operation Forager (the invasion of the Mariana and Palau islands) underwent preparation and execution at about the same time as D-Day, and few of the vehicles could be spared. Redeployment and retraining of amphibian tractor and amphibian tank battalions from the Pacific to European Theaters would have been another issue; drawing these units away could reduce the potential of troops in the Pacific to conduct landings. If LVTs were used on D-Day, it is presumed that only Army units would have been involved. In the first half of 1944, only a single Army amphibian tank battalion existed, the 708th. Activation and training of new units would also take time, up to a year.
The vast majority of LVT types were not armored at all, having only a thin steel hull.
| Version | Armor | Notes |
|---|---|---|
| LVT-1 | None (9 mm plates added to some vehicles' cabs before Tarawa) | No rear ramp: capacity 18 passengers |
| LVT-2 | None | No rear ramp; capacity 24 passengers |
| LVT(A)-2 | 6.5 mm on hull, 12.7 mm on cab | Armored version of the LVT-2; no rear ramp; capacity 24 passengers |
| LVT(A)-3 | Presumably 6.5 mm on hull, 12.7 mm on cab | Proposed armored version of the LVT-4; not produced |
| LVT-4 | None | Rear ramp; capacity 30 passengers |
| LVT(A)-1 | 6.5 mm on hull, 12.7 mm on cab, turret with armor characteristics of M3A1 light tank | Crew: 6 |
| LVT(A)-4 | 6.5 mm on hull, 12.7 mm on cab, turret with armor characteristic of M8 Howitzer Motor Carriage | Crew: 6 |
Another consideration is their personnel capacity; early LVTs (LVT-1, LVT-2, LVT(A)-2) could carry only 18 to 24 troops, and they had to jump over the side owing to the fact that there was no rear ramp, slowing their exit from the vehicle. Using these vehicles would have forced a reorganization of the agreed-upon assault infantry battalion structure (6 assault boats per rifle company and 5 support boats for the heavy weapons company, plus a command boat, each of 30 men) More waves of smaller-capacity vehicles slows the execution of the landing
The LVT-4, capable of carrying 30 men and having a rear ramp, only began production in December 1943. It is doubtful that the logistical priority for the new vehicle would have been given to the European Theater, as LVT-type vehicles were needed and had proved themselves for the frequent invasions of Japanese-held islands in the Pacific Theater.
The following is purely conjecture, since we do not have any idea how the LVT would have performed in the choppy, currented seas of Normandy. Landings in the Pacific were undertaken only in calm(er) conditions, in which the LVT performed fine. The LVT had quite low freeboard, in comparison to the LCVP and LCM, which were purely boats.
In combat, the LVT probably would have struggled against heavy German antitank and artillery fire. They probably would have performed a role similar to the LCVP or LCM, dropping off troops at the water's edge and retreating to pick up more. Transport versions of the LVT used this tactic in the Pacific, and generally did not advance beyond the beach, except to move cargo or retrieve wounded when combat had already moved inland. Advancing up the beach with a full load of troops in the rear compartment would have been suicidal; there was no overhead protection, and the installation of an armored roof was only theoretically possible on the (new) LVT-4. In places, they also would have been unable to progress beyond the "shingle", a slope of small slippery stones some distance up the beach, that was impossible for tracked vehicles to climb.
Sources:
Amtracs: US Amphibious Assault Vehicles, by Steven J. Zaloga