The DUKW, popularly called the DUCK, is a six-wheel-drive amphibious truck developed by the United States during World War 2 for transporting goods and troops over land and water and for use approaching and crossing beaches in amphibious attacks.

The DUKW was used in landings in the Pacific, in North Africa, and on D-Day on the beaches of Normandy. At Normandy alone, DUKW carried 18 million tons of supplies ashore in the 90 days after the landing that the enemy held all available ports.

The DUKW was developed by the National Defense Research Committee and the Office of Scientific Research and Development, but was originally rejected by the armed services. When a US Coast Guard patrol craft ran aground on a sandbar near Provincetown, Massachusetts, an experimental DUKW happened to be in the area for a scheduled demonstration a few days later. Winds up to 60 knots (110 km/h), rain, and heavy surf prevented conventional craft from rescuing the seven stranded coast guardsmen, but the DUKW had no trouble, and military opposition melted. Subsequently, DUKWs have proved their seaworthiness by crossing the English Channel and many other exploits at sea.

Although its designation as a DUKW may seem to be a military pun, in fact in the terminology developed for military vehicles in World War 2, the D indicates a vehicle designed in 1942, the U meant "utility (amphibious)", the K indicated all-wheel drive and the W indicated two powered rear axles. The DUKW was built around a conventional six-wheel drive military truck called the CCKW, with the addition of a watertight hull and a propeller. It was powered by a GMC Straight-6 engine of 270 cubic inches (4.4 L). The DUKW weighed 7.5 tons and operated at 6.4 mph (10 km/h) on water and 50 mph (80 km/h) on land. It was 31 feet (9.3 m) long, 8.25 feet (2.4 m) wide, and 8.8 feet (2.6 m) high with the folding canvas top up. More than 21,000 were manufactured.

The DUKW was the first vehicle which allowed the driver to inflate and deflate the tires from inside the cab, fully inflated for hard surfaces like roads and less inflated for softer surfaces - especially beach sand. This added to its great versatility as an amphibious vehicle and such arrangements are now a common feature on many military vehicles. The DUKWs were the only wheeled vehicles capable of operating on the beach at Iwo Jima, for instance.

After their success in WWII, the DUKWs were deactivated, only to be re-activated and sent to Korea as soon as the war there began. The DUKWs continued serving the United States Army until the mid-1960s.

Although DUKWs were used predominantly for the military, many were used by civilians: Police departments, fire stations and rescue units, just to name a few.