This was a British unsuccessful combined air and sea operation to intercept and destroy a Japanese submarine carrying important equipment and passengers from Germany to Singapore (11/13 November 1943).
'Type J-3' boats of the Imperial Japanese navy, the I-7 and I-8 were the largest Japanese submarines completed before the 'Ai' attack on Pearl Harbor precipitated the US entry into World War II. Based on the design of 'KD' class, the two submarines were committed to 'Ai', and then undertook patrol missions with Yokosuka E14Y 'Glen' floatplanes. As part of the 'Yanagi' programme, in 1933 I-8 completed a technology-exchange mission by sailing to German-occupied France and thence back to Japan.
The 'Yanagi' programme took place within the context of the Axis powers' Tripartite Pact agreement to implement exchanges of strategic materials, manufactured goods, information and key personnel between Germany, Italy and Japan. At first surface ships were employed to accomplish the exchanges in blockade-running operations, but when Allied interceptions had made that practice ho longer feasible, submarines were used. Only seven submarines attempted the trans-oceanic voyage: the Japanese I-30 in April 1942, I-8 in June 1943, I-34 in October 1943, I-29 in November 1943, I-52 in March 1944, and the German U-180 and U-511 in August 1943. Of these boats, I-30 was sunk by a mine, I-34 by the British submarine Taurus, I-29 by the US submarine Sawfish and I-52 by US Navy aircraft.
Under the command of Shinji Uchino, I-8 departed Kure on 1 June, accompanied by I-10 and the submarine tender Hie Maru. The cargo included two Type 95 'Long Lance' oxygen-propelled torpedoes, torpedo tubes, drawings of an automatic trim system and one E14Y floatplane, which was a new naval reconnaissance machine. A supplementary crew of 48 men, under the command of Sadatoshi Norita, was also embarked as the intended crew of the German 'Type IXC/40' submarine U-1224, which was to bring this boat to Japan for reverse engineering.
Arriving in Singapore nine days later, I-8 also took on board quinine, tin and raw rubber before heading for the Japanese base at Penang. On 21 July I-8 entered the Atlantic and, after battling through severe weather, on 20 August made a prearranged rendezvous with the German U-161, which transferred two German radio technicians and also a FuMB 1 'Metox' 600A radar detector. As the Japanese submarine entered the Bay of Biscay on 29 August, the Luftwaffe sent Junkers Ju 88 longer-range aircraft of Kampfgeschwader 40 to provide air cover, and the Japanese boat arrived in Brest two days later to a warm welcome. Parties and visits to Paris and Berlin were organised over a period of more than a month, and German news agencies announced that 'now even Japanese submarines are operating in the Atlantic'.
I-8 departed 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 rear Admiral Toshiyuki Yokoi, who was returning home after being the naval attaché to Berlin since 1940, Captain Hosoya, who had been the naval attaché to France since December 1939, three German officers and four radar and hydrophone technicians.
I-8 encountered severe weather in the South Atlantic, in the area off the Cape of Good Hope, and this delayed the boat’s arrival in Singapore. The boat had radioed her position to Germany, but the message was intercepted by the Allies, prompting an attack by anti-submarine aircraft, which failed. I-8 reached Singapore on 5 December, and finally returned to Kure in Japan on 21 December after a voyage of 34,550 miles (55600 km).