However, actual implementation of the new mission took another decade because the Marine Corps was preoccupied in Central America and the Navy was slow to start training in how to support the landings. The prototype advanced base force officially evolved into the Fleet Marine Force (FMF) in 1933. In 1939, during the annual Fleet Landing Exercises, the FMF became interested in the military potential of Andrew Higgins's design of a powered, shallow-draught boat. These LCVPs, dubbed the 'Higgins Boats', were reviewed and passed by the U.S. Naval Bureau of Construction and Repair. Soon, the Higgins boats were developed to a final design with a ramp, and were produced in large numbers.