From another article:
"Jerry cans" are so-named because they were originally designed and stockpiled for the German Wehrmacht during the build-up to WWII. Transporting and storing fuel in combat conditions was a critical problem as armies became mechanized, and Jerry cans were a secret project ordered by Hitler. They can be stacked with little wasted space. Their three handles allow easy carrying by either one or two people. The small built-in air space allows for expansion while minimizing condensation, and ensures that they'll float even when full. A traveling American engineer recognized the value of the ingenious design and stole three of them during an adventure that reads like a spy novel. They were subsequently delivered to America and Britain and reverse-engineered.