The Ford GPA "Seep" (seagoing jeep) was an amphibious version of the Ford GPW Jeep. The GPA was developed at the request of the Quartermaster Corps with the amphibious hull being designed by the Sparkman and Stephens Co., and Ford Motor Company taking care of the automotive engineering and assembly. The GPA engine, axles, transmission and transfer case were all basically the same as the Ford GPW Jeep, but the Seep was significantly longer and sported an 84-inch wheelbase. The spare tire and anchor were stored on the rear deck and a capstan winch was mounted on the front deck. A rudder and propeller at the rear of the GPA provided a means of locomotion in water. Unfortunately, the "Jeep-in-a-bathtub" was too much of a boat to be successful on land and too much of a car to be successful on water. The GPA wasn't well-liked by the soldiers who used it in the US Army. It was considered to be too unwieldy on land, and prone to swamping in any significant chop while carrying out its seagoing duties. It was said that the GPA would embarrassingly get stuck while trying to ford shallow water in situations where its terrestrial counterpart, the Willys MB Jeep, would plow right through. 12,778 were manufactured from 1942 to March, 1943 with a large number going to the Red Army via Lend-Lease. The Soviets, unlike their American allies, seemed to like the GPA well enough to manufacture the vehicle under licence as the GAZ 011 -- even continuing development beyond World War II.
Doyle, David. U.S. Military Vehicles Field Guide. Iola, WI: KP Books, 2005.
"GPA Amphibious 2-1/2 Ton 6x6 Truck." Olive-Drab.com. May 22, 2008. Oct. 6, 2010. http://www.olive-drab.com/idphoto/id_photos_gpa.php