At 07:01 on 4 May, "Yorktown" launched a first strike consisting of 12 TBD Devastator torpedo bombers and 28 SBD Dauntless dive bombers from a position about south of Guadalcanal. The aircraft began their attacks on Shima's ships anchored near Tulagi at 08:50, taking the Japanese ships by surprise and at anchor. "Okinoshima" and the two destroyers were positioned to provide a protective barrier for "Azumasan Maru" and "Kōei Maru" which were busy unloading troops and materiel. The three minesweepers had just got underway to support the Port Moresby invasion and were still near Tulagi. Although the U.S. pilots from the first strike claimed many bomb and torpedo hits on the anchored ships, they actually hit only "Okinoshima", causing minor damage, and "Kikuzuki", causing major damage. "Kikuzuki"—with the assistance of one of the subchasers—was beached on Gavutu in an attempt to keep her from sinking. During this time, all of the other ships weighed anchor and attempted to escape from the harbor. One U.S. dive bomber destroyed a Japanese Mitsubishi F1M2 "Pete" floatplane that attempted to take off during the attack.