The one thing that can be said about most amphibious automobiles is they tend to make lousy cars and worse boats.
Famous automobile designer J. Walter Christie experimented extensively with amphibious vehicles prior to WWII. None of them were successful enough to be put into production.
Several amphibious automobile designs came out of World War II
- The Volkswagen Type 166 Schwimwagen reconnaissance car was easily the most successful, because the Volkswagen's unique mechanical design of a platform frame combined with a torsion bar suspension and a lightweight air cooled engine allowed the Schwimwagen to be created through the simple expedient of bolting the mechanical and suspension components of a Volkswagen to a lightweight unibody hull. Volkswagen even sold some Schwimvagen on the civilian market after the war as they restarted the company by working off old stock. Over 30,000 type 166 Schwimwagen were built, making it the most produced amphibious car in history, though fewer than 200 remain.
- In contrast, the US attempt to make an amphibious jeep, the Ford GPA, was not considered a success because the Jeep's traditional body-on-frame design made it overweight. Ironically, the GPA was actually worse at fording shallow water than a regular Jeep as the extra bulk and mass of the boat-like hull tended to get it stuck in the mud. As a result most of them were lend-leased to the Soviet Union, where they actually proved quite popular as the Russian steppe is crisscrossed by many streams and rivers but very few roads. The Russians liked the GPA so much that they created an upsized version based on the GAZ 69 half ton truck called the GAZ 46, which was the first in a long line of similar vehicles for the Soviet military. While the GAZ 46 looks a lot like the GPA that inspired it, it's actually somewhat bigger and performs better due to the increased buoyancy. The so-called "Ducks" in Indiana Jones and the Kingdom of the Crystal Skull are actually fiberglass replicas of the GAZ 46 constructed on modern jeep chassis.
- The most successful of the WWII amphibians (and the likely source of Indy's miss-identification of the GAZ as a duck) was actually not a car at all, it was the GMC DUKW 2-1/2 ton 6x6 amphibious truck, AKA the "Duck". Like the GAZ 46 it benefited greatly from the increased buoyancy that came from a larger hull, and the additional traction from larger wheels and tires. Unlike the GPA and GAZ it was actually buoyant enough to be used on the open ocean. Interestingly, the DUKW designation was the General Motors model code: "D" for designed in 1942, "U" for "utility", "K", for all-wheel drive, and "W" for dual rear axles. The fact that it worked out to "Duck" was purely coincidental. (GM still uses "K" for all wheel drive trucks)
- In the modern day, the Watercar
Panther. It is basically a cross between a jeep and a jetboat, and performs very well as both.
