In a bid to defy the American blockade, Vice-Admiral Boshirō Hosogaya, in charge of the 5th Fleet and the northern theatre of operations, assembled a high-speed convoy with two fast merchant ships Asaka Maru (7399 GRT) and Sakito Maru (7158 GRT) and a slower transport, the Sanko Maru (5491 GRT). The latter and her escort, the destroyer Usugumo, were to made a rendezvous with the main force south of the Kommandorski Island. The ships carried key materiel needed to complete the building of an all-weather airstrip at Attu.
