Commanded by Shinji Uchino, I-8 departed Kure harbor on 1 June 1943, accompanied by I-10 and the submarine tender Hie Maru. Their cargo included two of the famed Type 95 oxygen-propelled torpedoes, torpedo tubes, drawings of an automatic trim system and a new naval reconnaissance plane, the Yokosuka E14Y. A supplementary crew of 48 men, commanded by Sadatoshi Norita, was also packed into the submarine, intended to man the German submarine (U-1224, a Type IXC/40 U-boat) and bring her back to Japan for reverse engineering.