U-168 was a Type IXC/40, a long-range ocean-going submarine designed to operate far from German waters. Her keel was laid down on March 15, 1941, at the Deutsche Schiff- und Maschinenbau AG shipyard in Bremen. She was launched on March 5, 1942, and commissioned on September 10 under the command of Kapitanleutnant Helmuth Pich. At 76.76 meters long with a surface displacement of 1,144 tonnes, she was slightly larger than the earlier Type IXC boats and could travel an extraordinary 13,850 nautical miles at 10 knots while surfaced -- range enough to reach the Indian Ocean from Europe without refueling. She carried 22 torpedoes, a 10.5-centimeter deck gun with 180 rounds, and anti-aircraft weapons. Her crew numbered 48 men, and they would need every kilometer of that range.

By 1943, Germany was sending U-boats to operate from Japanese-controlled ports in Southeast Asia, part of the so-called Monsoon Group. These submarines hunted Allied shipping in the Indian Ocean, where convoy protection was thinner than in the Atlantic and targets were plentiful. U-168 arrived at Penang in British Malaya -- by then under Japanese occupation -- in November 1943, surviving an attack by a Canadian Catalina flying boat of No. 413 Squadron RCAF along the way. Four 250-pound depth charges tumbled down but missed. Penang became her forward base, a port where German submariners shared docks with Japanese warships in one of the war's stranger alliances of convenience.

U-168's third patrol, departing Penang on February 7, 1944, was her most productive and her most ruthless. South of Ceylon -- present-day Sri Lanka -- she fired three torpedoes at a British salvage vessel on February 14. One malfunctioned, but the other two sent the ship to the bottom. The next day, she sank the Greek merchant ship Epaminondas C. Embiricos roughly 130 nautical miles north of Addu Atoll in the Maldives. Pich took the Greek vessel's master and chief engineer prisoner and handed them to the Japanese. The captain's subsequent captivity had an unintended bureaucratic consequence: British authorities could not discipline him for abandoning an undamaged ship and leaving it stationary for two hours in violation of standing wartime orders. On February 21, U-168 damaged the Norwegian tanker Fenris with her last torpedo west of the Maldives but had expended all her deck gun ammunition and could not finish the job. Fenris limped into Bombay under her own power. The submarine returned to Batavia on March 24, her torpedo tubes empty.

What happened next was a consequence of coalition warfare and its inherent vulnerabilities. When U-168 departed Batavia on October 5, 1944, for her fourth patrol, standard operating procedure required her to share navigational details with the Japanese military so their own forces would not attack her by mistake. The submarine's departure time, course, and speed were transmitted through Japanese channels. Allied codebreakers at FRUMEL -- the Fleet Radio Unit, Melbourne, which specialized in breaking Japanese naval codes -- decrypted the message that same day. The intelligence was actionable and time-sensitive. A Free Dutch Forces submarine commanded by Lieutenant Commander H. Goossens received orders to intercept. The hunt was measured in hours, not days.

Shortly after dawn on October 6, 1944, Goossens's submarine spotted U-168 on a steady easterly course in the Java Sea, exactly where the decrypted coordinates said she would be. The Dutch boat fired a spread of six torpedoes. The attack killed 23 of U-168's crew. Twenty-seven others were captured, including Pich, who survived his submarine's destruction. The sinking carried a particular irony: a German U-boat, operating from a Japanese port, destroyed by a Dutch submarine acting on intelligence gleaned from Japanese communications -- the war's tangled alliances turned inside out in a single engagement. In late 2013, divers located what they believed to be U-168's wreck on the floor of the Java Sea, the hull still holding the remains of the 23 men who went down with her. The site, known locally as Taka Pesawat, lies in waters that were once among the most contested on earth and are now quietly forgotten by all but the fish and the occasional diver willing to make the trip.