World War Two saw a reinstatement of the critical value of Garden Island to national defence and the facility immediately undertook extensive vessel repairs and modification work. The importance of the facility was demonstrated on 31 May 1942 when the Japanese Imperial Navy attacked Sydney Harbour with a fleet of five I-class ocean going submarines and three midget's. The principle targets were the heavy ships in port at that time, including the cruiser USS "Chicago" tied up at No.2 Buoy on the eastern side of Garden Island. While the raid was a failure with no significant losses, bar two of the midget submarines, the island Depot Ship, the ex-ferry , was destroyed by torpedo alongside Garden Island, killing 21 sailors. The importance of this tragedy is remembered with a commemorative plaque on the eastern side of Garden Island, annual commemoration ceremonies at that historic spot and the naming of the HMAS Kuttabul base.