'Marco Polo' was a German largely unrealised plan for collaborative political and military ventures with Japan (10 May 1943/44).

An early step toward this objective was the passage of Kapitänleutnant Fritz Schneewind’s U-511, which departed Germany in April bound for Penang off the west coast of occupied Malaya for onward passage to Kure and transfer to Japanese control as a personal gift from Adolf Hitler to Emperor Hirohito.

[3]U-511's final patrol took her all the way to Japan, as part of the ongoing programme of technological exchange. The boat carried additional personnel, including the German ambassador to Tokyo, the Japanese naval attaché in Berlin and German scientists and engineers. Departing Lorient on 10 May 1943, the boat travelled through the Atlantic and passed round the Cape of Good Hope into the Indian Ocean, where it made two 'kills'.

The first attack was made at 09.42 on 27 June, when the boat scored two torpedo hits the unescorted 7,194-ton US 'Liberty' ship Sebastian Cermeno, disabling the ship’s engines and killing one officer and two men. The survivors abandoned ship in five lifeboats. Ten minutes after being hit, the ship sank. The U-boat surfaced and questioned the survivors before leaving. The lifeboats lost contact with each other, but all were eventually rescued by Allied ships, apart from one boat which made its own way to Madagascar.

The boat’s second success came on 9 July when it torpedoed the 7,176-ton US 'Liberty' ship Samuel Heintzelman, which was carrying a cargo of 5,644 tons of ammunition and general cargo. The U-boat dived after firing and did not directly observe the results, but heard explosions. On surfacing, the boat’s crew saw no trace of the ship, but only floating debris. There were no survivors from the 75 men on board. The ship was reported missing, and was at first believed to have been sunk by a Japanese surface raider. On 30 September, wreckage from the ship was discovered off the Maldive islands group,

The boat arrived in Kure on 7 August after a voyage lasting 90 days, and was handed over to Japan on 16 September for service as the Imperial Japanese navy’s Ro-500. After various ceremonies, the boat’s crew was transported to the German submarine base at Penang, off the west coast of Malaya, by surface vessel.