The DD (Duplex Drive) floating Sherman tanks of D-Day.
DD tanks worked by erecting a canvas 'flotation screen' around the tank, which enabled it to float in water. 'Duplex drive' refers to the fitted propellers allowing propulsion through water, which supplemented the usual track propulsion used when the flotation screens were lowered upon landing to fight as an ordinary tank. The DD tanks were one of the many specialized assault vehicles, collectively known as Hobart's Funnies, devised to support the planned invasion of Europe.

[img alt="An example of a surviving Duplex Drive tank used in the landings on Normandy, France on 6 June, 1944. Operation Overlord or D-Day.
The window on this tank was put there for display purpose. The tanks used back then didn't have windows on them."]https://cimg1.ibsrv.net/gimg/www.crossfireforum.org-vbulletin/780x438/tank_f20f1044ead4d33f59b10389de4e9f349d497305.jpg[/img]
An example of a surviving Duplex Drive tank used in the landings on Normandy, France on 6 June, 1944. Operation Overlord or D-Day. The window on this tank was put there for display purpose. The tanks used back then didn't have windows on them.

A collection of Duplex Drive tanks.