I-8 left Brest on 5 October, with a cargo of German equipment, such as: machine guns, bomb sights, a Daimler-Benz torpedo boat engine, marine chronometers, radars, sonar equipment, anti-aircraft gunsights, electric torpedoes, and penicillin. The submarine also transported Rear Admiral Yokoi, naval attaché to Berlin since 1940; Captain Hosoya, naval attaché to France since December 1939; three German officers and four radar and hydrophone technicians.