It was imperative for Japanese commanders to hold Saipan. The only way to do this was to destroy the U.S. Fifth Fleet, which had 15 fleet carriers and 956 planes, 7 battleships, 28 submarines, and 69 destroyers, as well as several light and heavy cruisers. Vice Admiral Jisaburo Ozawa attacked with nine-tenths of Japan's fighting fleet, which included nine carriers with 473 planes, 5 battleships, several cruisers, and 28 destroyers. Ozawa's pilots were outnumbered 2:1 and their aircraft were becoming or were already obsolete. The Japanese had considerable antiaircraft defenses but lacked proximity fuzes or good radar. With the odds against him, Ozawa devised an appropriate strategy. His planes had greater range because they were not weighed down with protective armor; they could attack at about 480 km (300 mi)[citation needed], and could search a radius of 900 km[citation needed] (560 mi). U.S. Navy Hellcat fighters could only attack within 200 miles (320 km) and only search within a 325-mile (523 km)[citation needed] radius. Ozawa planned to use this advantage by positioning his fleet 300 miles (480 km)[citation needed] out. The Japanese planes would hit the U.S. carriers, land at Guam to refuel, then hit the enemy again when returning to their carriers. Ozawa also counted on about 500 land-based planes at Guam and other islands.

What was it imperative for the Japanese to hold?