With the outbreak of general war, the mission of the 6th Fleet expanded to include shipping interdiction and mine laying. A few specialized missions, such as the Attack on Sydney Harbour with the use of midget submarines were also undertaken. The 6th fleet cooperated briefly with the Kriegsmarine (German navy) in the Indian Ocean in operations to interdict British commerce from its base in Penang, but these missions were few. The IJN General Staff placed more emphasis on ambush operations of Allied capital ships. In 1942, Japanese submarines were credited with sinking two aircraft carriers, one cruiser and several destroyers, as well as damaging one aircraft carrier and two battleships.