German submarine U-1224 was a Type IXC/40 U-boat of Nazi Germany's Kriegsmarine built for service during World War II.

Ro-501 was sunk on 13 May 1944 on her way to Japan by a U.S. Navy anti-submarine hunter-killer group, about 500 nautical miles off Cape Verde in the Atlantic, after spending two days trying to evade the pursuers.

The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of 4,400 metric horsepower (3,240 kW; 4,340 shp) for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of 1,000 shaft horsepower (1,010 PS; 750 kW) for use while submerged.

[5] U-1224 became part of the transfer of technology and knowledge missions that existed between Japan and Germany during World War II.

A full crew of Japanese personnel was to be trained by the Germans to operate a U-boat, after which the boat would be gifted to Japan.

[5][7] The first, U-511, was code-named "Marco Polo I" and departed Germany in May 1943, carrying along with its German crew several passengers that included engineering officers, the Japanese naval attaché Naokuni Nomura, and the diplomat Ernst Woermann, who was going to take up his post as German ambassador to the pro-Japanese collaborationist Wang Jingwei regime in China.

At the end of March 1944, several Japanese naval engineering officers that had been studying in Germany, led by Captain Tetsuhiro Emi, arrived in Kiel, where they boarded Ro-501 and departed for Japan along with some war materials.

They also took with them mercury, lead, steel, uncut optical glass and aluminum, along with the blueprints to construct a Type IX submarine and a Messerschmitt Me 163 "Komet" jet fighter.

[4][6] U-1224 arrived in Norway on 30 March 1944 to refuel, and continued on its journey in early April, initially along with the German submarine U-859, which was also carrying a cargo of war material bound for Japan.

This transmission was detected by the American ships with their high-frequency direction finding ("Huff-Duff") equipment, enabling them to pinpoint the submarine's location.

[4] In early July 1944, the German naval attaché in Japan, Paul Wenneker, sent a message to Berlin asking about the status of Ro-501, to which he received the answer that U-boat Command had not heard from the submarine since 11 May.

[4][9] The final resting place of U-1224/Ro-501 is 500 nautical miles (930 km; 580 mi) west-northwest of the Cape Verde islands at 18°7′59″N 33°12′59″W / 18.13306°N 33.21639°W / 18.13306; -33.21639 in 2,900 feet (880 m) of water.