About 500 British Terrapin Mark I amphibious vehicles were produced. Morris Commercial built them during 1943–1944 for wartime transport and river-crossing duties.
The Terrapin was commissioned because Britain faced a shortage of American DUKW amphibious trucks. Thornycroft designed the vehicle, officially called the 4-ton amphibian, while Morris Commercial handled production. Its purpose was to move supplies and troops from ships to shore and across inland waterways.
The Mark I used two Ford V8 engines mounted side by side, with each engine driving the wheels on one side. Two rear propellers provided water propulsion. This unusual layout helped create an amphibious 8x8 carrier, but it also divided the cargo space and gave the centrally positioned driver poor visibility.
Terrapins served with Royal Engineer assault teams of the 79th Armoured Division. They saw action during the Battle of the Scheldt and later helped carry British and Canadian troops across waterways. A longer Mark II reached prototype stage, with only five built, so the commonly cited production figure of 500 refers to the main Mark I series.