<P> A map of Okinawa's airfields, 1945 </P> <P> The United States Navy's Task Force 58, deployed to the east of Okinawa with a picket group of from 6 to 8 destroyers, kept 13 carriers (7 CVs and 6 CVLs) on duty from March 23 to April 27 and a smaller number thereafter . Until April 27, a minimum of 14 and up to 18 escort carriers (CVEs) were in the area at all times, and until April 20 British Task Force 57, with 4 large and 6 escort carriers, remained off the Sakishima Islands to protect the southern flank . </P> <P> The protracted length of the campaign under stressful conditions forced Admiral Chester W. Nimitz to take the unprecedented step of relieving the principal naval commanders to rest and recuperate . Following the practice of changing the fleet designation with the change of commanders, US naval forces began the campaign as the US 5th Fleet under Admiral Raymond Spruance, but ended it as the 3rd Fleet under Admiral William Halsey . </P> <P> Japanese air opposition had been relatively light during the first few days after the landings . However, on April 6, the expected air reaction began with an attack by 400 planes from Kyushu . Periodic heavy air attacks continued through April . During the period March 26--April 30, twenty American ships were sunk and 157 damaged by enemy action . For their part, by April 30, the Japanese had lost more than 1,100 planes to Allied naval forces alone . </P>

How many ships were used in the battle of okinawa