"FMC/GDLS LVTP-7/AAVP-7
Notes: Though development of what would become the AAVP-7 began in 1964, it was the first year of US involvement in Vietnam that really brought home to the Marines the shortcomings of the LVTP-5 series and the need for a better amphibious APC. The Marines quickly discovered that the LVTP-5 had a number of problems – it’s torsioelastic suspension, while it provided a comfortable ride over water and shore conditions such as rocks, sand, and reefs, was ill-suited for long trips and thus subject to frequent breakdowns. The LVTP-5 used the transmission and engine of the M-48 main battle tank – great for power, but not suited in the LVTP-5’s configuration; it could take a day of more to replace the power pack, and even routine service could require pulling out large amounts of the power pack just to get to the components to be serviced. Perhaps the greatest problem with the LVTP-5 as used in Vietnam lay with the fuel system; the tanks were under the floor, the engine ran on gasoline, and as the entire vehicle was lightly armored in the first place, even an antipersonnel mine explosion could sometimes turn the interior into a fiery slice of hell.
Because many of the LVTP’s problems were caused by improper employment of the vehicle, the Marines wanted something new that could take on roles Amtracs of the past could not. One of the first things to go was the torsioelastic suspension, replaced with a conventional torsion bar suspension on what was then called the LVTP-7 (later changed to AAVP-7). The armor protection was considerably upgrade, using the same 5083 aluminum armor that was used on the M-113 series. The engine chosen was a supercharged 400-horsepower 8V53T diesel truck engine with an HS-400 transmission; more importantly, the powerpack was a unified unit that could easily be lifted out of the vehicle in a matter of minutes with the proper equipment. The transmission was semiautomatic – it required no clutch, but still required gear selection on the part of the driver. The tracks were almost 54 centimeters wide for traction on soft sand as well as marshy conditions, and water propulsion was provided by two waterjets at the rear. Many other ideas were added, thrown out, or modified, and that, combined with political wrangling, meant that first deliveries of the LVTP-7 did not occur until 1972."