During 1942 and 1943, Japanese submarines periodically operated in the waters surrounding Australia. A force of midget submarines raided Sydney Harbour on the night of 31 May – 1 June 1942 and attacks on merchant shipping travelling off the east coast began several days later. These attacks continued until August 1942, when the Japanese submarine force was redeployed. The "I-174" made a 24-day patrol off Australia in July and August 1942, but did not attack any ships. In response to the Japanese attacks, the Australian naval authorities ordered that all ships with a displacement of more than 1,200 tons and a maximum speed of less than 12 knots travel in escorted convoys from 8 June. These convoys were successful in minimising losses, and no escorted ships were sunk off Australia during 1942.