https://en.wikipedia.org/wiki/Consolidated_PBY_Catalina

The PBY was originally designed to be a patrol bomber, an aircraft with a long operational range intended to locate and attack enemy transport ships at sea to disrupt enemy supply lines.[5] With a mind to a potential conflict in the Pacific Ocean, where troops required resupply over great distances, the U.S. Navy invested millions of dollars in the 1930s developing long-range flying boats, which had the advantage of being able to land in any suitable waters.