U-847 was damaged by ice in the Denmark Strait and headed for France, but it was decided to use her as a tanker. Between 12 and 24 August the boat refuelled U-66, U-415, U-230, U-653, U-257, U-172 and U-508.

U-847 was a rather inexperienced boat on its first war cruise: the commanders of the boats which took on fuel reported that their replenisher made excessive use of its radio, and the boat was sunk by air attack on 27 August.

Of the initial 11 'Monsun' (i) boats, therefore, four were sunk on passage and another two, of which one was sunk, diverted on emergency refuelling duties. Thus only five boats managed to break through. U-168, U-183, U-188, U-532 and U-533 reached the Indian Ocean without further trouble, and between 11 and 13 September refuelled at sea from the surface oiler Brake operating from Penang, the rendezvous point being 450 miles (725 km) to the south of Mauritius and the refuelling being completed without incident.

Meanwhile Japanese submarines already started to operate in the Arabian Sea during August 1943, and arrangements were made to avoid incidents between U-boats and Japanese submarines, attacks on other submarines being strictly forbidden.

Eventually the 'Monsun' (i) boats were disposed with U-168 operating off Bombay (sank one ship), U-183 between the Seychelles and the African coast (no sinkings), U-188 in the Gulf of Oman (sank three ships), U-532 off the south and west coasts of India (sank five ships), and U-533 in the Gulf of Aden (lost there on 6 October to air attack). U-188 experienced torpedo failures as a result of high temperatures, which adversely affected the torpedo batteries.

The surviving 'Monsun' (i) boats had reached Penang by the beginning of November 1943. The commanders of U-168 and U-183 had been affected by the strain of the long voyage, and the commander of U-183 was later replaced by Schneewind of U-511.

The German naval authorities had meanwhile decided to despatch a second wave of 'Monsun' (i) boats as attrition replacements. These five boats were Korvettenkapitän Walter Burghagen’s U-219, Kapitänleutnant Alfred Eick’s U-510, Korvettenkapitän Wilhelm Rollman’s U-848, Kapitänleutnant Heinz-Otto Schultze’s U-849 and Korvettenkapitän Klaus Ewerth’s U-850. These boats departed German, Norwegian and French bases between September and November. It was planned that U-219 would lay mines off Cape Town and Colombo, but the boat was recalled for service as a tanker and reached a French base in January 1944. U-848 and U-849 were sunk off Ascension island, and U-850 off the Azores islands group: all three boats succumbed to air attack. U-510 refuelled from U-219 and reached the Indian Ocean, where it sank six ships (34,013 tons) in February and March 1944. In the Indian Ocean U-510 joined the boats operating from Penang. The first of these was Kapitänleutnant Wilhelm Spahr’s U-178, soon followed by Junker’s U-532, Ludden’s U-188, Pich’s U-168 and Schneewind’s U-183. U-178 and U-510 refuelled from the surface oiler Charlotte Schliemann on 28 January at a location about 100 miles (160 km) to the south-east of Mauritius island.

The size of flotilla was limited to just five boats by Penang’s lack of dockyard capacity, and the 'Monsun' (i) boats were so short of torpedoes that U-532, U-188 and U-183 were ordered to embark strategic materials and return home via the patrol areas in the Indian Ocean. U-532 was also to refuel from Charlotte Schliemann but was prevented from this on 11 February by adverse weather at a location some 950 miles (1530 km) to the east of Madagascar. The oiler was then detected by the Allies while refuelling U-532 and was scuttled: 41 survivors were rescued by the British destroyer Relentless and others were recovered by U-532, which later came under depth charge attack for three days.

U-178 transferred some fuel to U-532 on 26 February and departed for France. U-178 was attacked by aircraft on 8 March off the Cape of Good Hope but survived. It was later to meet the eastbound transport UIT-22 but the latter, an ex-Italian submarine, was sunk by aircraft on 11 March. The German boat reached Bordeaux in France with its engines only just working.

The remaining five boats continued their operations. Another refuelling was scheduled from the oiler Brake in March 1944. This time U-532, U-188 and U-168 searched the area for some time before the scheduled rendezvous, and on 12 March U-188 and U-532 managed to refuel before adverse weather interrupted the operation. Later during the day Brake was detected and then scuttled by her crew, the survivors being rescued by U-168. The boats now had to share fuel among themselves, and U-168, U-532 and U-183 were eventually compelled to remain in the Far East for lack of fuel.

Only U-188 could proceed back to Europe, reaching France on 19 June only to be paid off and later scuttled.

One of the reasons for disappointing results achieved by the 'Monsun' (i) boats was the quality and quantity of the torpedoes available at Penang. These had been offloaded from German armed merchant cruisers and delivered by blockade-runners, and then suffered badly from the long period of storage in the tropics. To overcome this problem, special 'Type VIIF' torpedo transport boats were despatched with fresh torpedoes and spares.

More operational boats were also sent to the Far East: in order of despatch between 2 January 1944 and 1 April 1945, these were Kapitänleutnant Heinz Buchholz’s U-177, Oberleutnant Karl Albrecht’s U-1062, Kapitänleutnant Heinz-Wilhelm Eck’s U-852, Oberleutnant Günter Leupold’s U-1059, Kapitänleutnant Oskar Herwartz’s U-843, Kapitänleutnant Hans-Joachim Brans’s U-801, Korvettenkapitän Hannes Weingärtner’s U-851, Fregattenkapitän Kurt Freiwald’s U-181, Korvettenkapitän Eitel-Friedrich Kentrat’s U-196, Kapitänleutnant Peter Schrewe’s U-537, Kapitänleutnant Johann Jebsen’s U-859, Fregattenkapitän Paul Buchel’s U-860, Oberleutnant Burkhard Heusinger von Waldegg’s U-198, Kapitänleutnant Jürgen Oesten’s U-861, Oberleutnant Wilhelm Gerlach’s U-490, Kapitänleutnant Heinrich Timm’s U-862, Kapitänleutnant Dietrich von der Esch’s U-863, Oberleutnant Rolf Riesen’s U-180, Oberleutnant Friedrich Steinfeldt’s U-195, Korvettenkapitän Walter Burghagen’s U-219, Korvettenkapitän Erwin Ganzer’s U-871, Kapitänleutnant Ralf-Reimar Wolfram’s U-864 and Kapitänleutnant Johann-Heinrich Fehler’s U-234. The boats included the Schnorchel-equipped U-180, U-195, U-219, U-863, U-864 and U-234.

U-852 sank the 4,695-ton Greek Peleus on 13 March 1944 and then machine-gunned the survivors in the water. The U-boat’s commander and officers were later captured, tried and sentenced to death in the only proven case of a U-boat machine-gunning survivors.

U-198 reached the Indian Ocean, achieved some success, but was sunk by anti-submarine vessels with air assistance.

U-859 also reached Indian Ocean patrol, achieved some success but was sunk by a British submarine off Penang.

U-843 was damaged by aircraft in the Atlantic but reached Penang.

U-859 was torpedoed by an Allied submarine off Penang after a six-month patrol in which it scored several hits.

U-180 and U-195 were the only 'Type IXD/1' class boats with experimental and unreliable fast-running diesel engines. They were therefore converted to transports with new diesels and with U-219, a minelayer also adapted as a transport, left Europe as a part of the U-boat evacuation of French ports. All three boats headed for the Far East, and while U-180 was mined, the other two reached Djakarta (Batavia) in the Japanese-occupied Netherlands East Indies.

U-490 was sent to the Far East to make up for the loss of supply ships in the Indian Ocean. U-861 initially operated off the Brazilian coast. U-537 was refuelled by U-183 on 25 June 1944. Of the boats listed above, U-852, U-198, U-181, U-537, U-196, U-862, U-861 and U-859 scored hits. The sinkings in the Indian Ocean started on 1 April 1944 and ended in September 1944 when all the boats were either in port or had been sunk. The boats' peak period was July and August 1944.

An appreciable percentage of the U-boat effort in the Far East was shifted gradually from combat to transport missions. Some of the boats, including U-180, U-195, U-219 and U-234, were permanently converted as transports. The importance to Germany of the transport missions can be judged from the fact that even in the spring 1945 U-boats were still sailing to the Far East, some of them with very interesting cargoes. Kapitänleutnant Johann-Heinrich Fehler’s U-234, for instance, had departed a Norwegian base on 16 April 1945 bound for Japan with extremely important cargo (drawings, a crated Messerschmitt Me 262 jet fighter, 1,235 lb [560 kg] of uranium oxide, several senior German experts on various technologies, and two Japanese officers), but on hearing of the end of the war Fehler opted to head for the USA and surrender.

Oberleutnant Theodor Petersen’s U-874 and Kapitänleutnant Georg Preuss’s U-875 were loading some 170 tons of mercury, lead and optical glass, but did not leave European waters before the end of the war.

Very few of the 'Monsun' (i) boats departed on patrols intended to end in Far Eastern rather than European bases. U-168, U-183 and U-532 all departed on patrols early in 1944, but it was planned that the U-183 and U-532 should arrive back in European waters. U-181 and U-183 departed Penang on 10 October and 17 May 1944 respectively and ended their patrols at Djakarta and Penang on 5 January 1945 and 7 July 1944, while U-862 departed from and returned to Djakarta on 18 November 1944 and 15 February 1945 respectively. U-183 operated off the south coast of India, on about 25 June refuelled the eastbound U-537, and sank just one ship. U-181 sank only one ship. U-862 operated in the Pacific off Australia and came close to Sydney as it sank the 7,180-ton US Robert J. Walker off southern New South Wales near Montague island at a location about 160 miles (255 km) from Sydney on 24 December 1944. After this the boat did not move farther north, to the Sydney area, but retraced its route back to the Indian Ocean.

U-862 was the only German boat to operate in the Pacific.

From the middle of 1944 the Indian Ocean had become as dangerous for U-boats as the Atlantic. The base at Penang had very limited resources, to the severe detriment of German operations, and supply ships could no longer operate in the Far East. This meant that U-boats had to spend a high proportion of their endurance on passage and only a small proportion in the operational area.

The German naval commander at Penang, Fregattenkapitän Wilhelm Dommes, was ordered to move to Djakarta, which offered better access to oil and the Indian Ocean. All the boats were to be prepared for sea, packed with as much cargo and torpedoes as possible and to be sent home. As the French ports were no longer available, the boats were to go to Norway, being refuelled by other submarines when necessary.

The difficulty of returning to Europe from the Far East can be seen from the experience of first-wave 'Monsun' (i) boats early in 1944: only U-188 made it home without undue difficulty, U-183 and U-532 had to return to Far Eastern bases as a result of fuel difficulties, and U-178 came under heavy air attack on the way back home.

Since a time early in 1944 the passage back to Europe had become increasingly dangerous and was thus achieved by only a few boats. One of the main problems was that Allied air power was rampant in the Indian and Atlantic Oceans, and most of the 'Monsun' (i) boats were not fitted with a Schnorchel, lacked the most advanced radar and radar-detection equipment, and generally possessed only indifferent anti-aircraft armament.

Oberleutnant Karl Albrecht’s U-1062 was sunk on 5 October 1944, Kapitänleutnant Helmut Pich’s U-168 was sunk on 4 October 1944, Fregattenkapitän Kurt Freiwald’s U-181 returned to Djakarta on 5 January 1945, Kapitänleutnant Peter Schrewe’s U-537 was sunk on 9 November 1944, Oberleutnant Werner Striegler’s U-196 was sunk on 30 November 1944, Kapitänleutnant Alfred Eick’s U-510 returned to Djakarta on 3 December 1944, Kapitänleutnant Oskar Herwartz’s U-843 reached Bergen in Norway on 3 April 1945, Kapitänleutnant Alfred Eick’s U-510 reached a French base on 24 April 1945, Fregattenkapitän Otto-Heinrich Junker’s U-532 surrendered at the time of Germany’s defeat, Kapitänleutnant Jürgen Oesten’s U-861 reached a Norwegian base on 18 April 1945, Oberleutnant Friedrich Steinfeldt’s U-195 arrived in Djakarta on 3 March 1945, and Kapitänleutnant Fritz Schneewind’s U-183 was sunk on 24 April 1945.

U-181 got as far as South Africa but had to return with a propeller shaft problem after sinking one ship. Engine trouble forced U-510 to return to Djakarta on her first attempt to return, in the process demonstrating the poor labour and poor quality fuel available in the Far East; on its second attempt U-510 ran out of fuel and had to surrender at St Nazaire: this boat had the distinction of sinking the last ship to be sunk by a submarine in the Indian Ocean when it torpedoed the 7,136-ton Canadian Point Pleasant Park on 23 February 1945.

While proceeding home U-843 refuelled from the eastbound U-195 on about 20 December 1944, reached Norway but was then sunk while attempting to transit the Kattegat into the Baltic. U-532 scored hits on the way home but eventually surrendered at sea and was brought to Liverpool: the boat’s cargo comprised 110 tons of tin, 8 tons of tungsten, 4 tons of molybdenum and smaller amounts of selenium, quinine and crystals plus 8 tons of rubber in tube-like containers. The boat had been refuelled on about 20 February 1945 by U-195, which then returned to Djakarta as its engines were not capable of enduring the long journey home.

The returning 'Monsun' (i) boats were often sunk by Allied submarines patrolling off the German bases. This was the case of U-168 (sunk by the Dutch submarine Zwaardvis), U-537 (US submarine Flounder), and U-183 (US submarine Besugo).

During 1944 only two out of a planned 14 U-boats reached Europe from the Far East with cargoes: these were U-178 and U-188, whose efforts were supplemented by that of one Japanese submarine). In 1945 again only two U-boats came home: these were U-843 and U-861, each carrying 100 tons of zinc. U-843 was later sunk in the Belt when transferring to Germany. U-510 and U-532 did manage to reach Europe and surrender.