and a major fleet engagement. Fleet Problem XVI Held in May 1935 in the northern Pacific off the coast of Alaska and in waters surrounding the Hawaiian Islands, this operation was divided into five distinct phases, modeled on proposals for a US offensive in the Pacific. The largest of these interwar exercises, Fleet Problem XVI was seen as a provocation by Japan, which conducted its own major exercise in response. Fleet Problem XVII This problem took place off the west coast of the U.S., Central America, and the Panama Canal Zone in the spring of 1936. It was a five-phase exercise devoted to preparing the fleet for anti-submarine operations, testing communications systems, and training of aircraft patrol squadrons for extended fleet operations, and pitted the Battle Force against the submarine-augmented Scouting Force. Fleet Problem XVIII This exercise was held in May 1937 in Alaskan waters and in the vicinity of the Hawaiian Islands and Midway, practicing the tactics of seizing advanced base sites—a technique later to be polished to a high degree into close support and amphibious warfare doctrines. Fleet Problem XIX This operation in April and May 1938 gave the navy added experience in search tactics; in the use of submarines, destroyers, and aircraft in scouting and attack; in the dispositions of the fleet; and in the conduct of a major fleet battle. In addition, the exercise again dealt with the matter of seizing advanced fleet bases and defending them against minor opposition. Fleet Problem XIX also tested the capabilities of the Hawaiian Defense Force, augmenting it with fleet units to help to defend the islands against the United States Fleet as a whole. The last phase of the exercise exercised the fleet in operations against a defended coastline. Fleet Problem XX Took place in February 1939 in the Caribbean and Atlantic, and observed in person by President Franklin Roosevelt. The exercise simulated the defense of the East Coast of the United States and Latin America by the Black team from the invading White team. Participating in the maneuvers were 134 ships, 600 planes, and over 52,000 officers and men. Fleet Problem XXI Problem XXI was the first since Problem IX in 1928 that did not involve almost all of the active fleet. World War II had already begun in Europe, and the US Navy had been called upon to provide "Neutrality Patrols" in the Atlantic Ocean. Over 60