Construction

U-28 was ordered by the Kriegsmarine on 1 April 1935 as part of the German Plan Z and in violation of the Treaty of Versailles. Her keel was laid down in the AG Weser shipyard in Bremen as yard number 909 on 2 December 1935. After about ten months of construction, she was launched on 14 July 1936 and commissioned into the Kriegsmarine as the third Type VIIA submarine on 12 September 1936 under the command of Kapitänleutnant Wilhelm Ambrosius.^[1]

Design

Like all Type VIIA submarines, U-28 displaced 626 tonnes (616 long tons) while surfaced and 745 t (733 long tons) when submerged. She was 64.51 m (211 ft 8 in) in overall length and had a 45.50 m (149 ft 3 in) pressure hull. U-28's propulsion consisted of two MAN 6-cylinder 4-stroke M 6 V 40/46 diesel engines that totaled 2,100–2,310 PS (1,540–1,700 kW; 2,070–2,280 bhp). Her maximum rpm was between 470 and 485. The submarine was also equipped with two Brown, Boveri & Cie GG UB 720/8 electric motors that totaled 750 PS (550 kW; 740 shp). Their maximum rpm was 322. These power plants gave U-28 a maximum speed of 17 knots (31 km/h; 20 mph) while surfaced and 8 knots (15 km/h; 9.2 mph) when submerged. She had a range of 6,200 nmi (11,500 km; 7,100 mi) while traveling at 10 knots (19 km/h; 12 mph) on the surface and 73–94 nmi (135–174 km; 84–108 mi) at 4 knots (7.4 km/h; 4.6 mph) when submerged.

The U-boat's test depth was 220 m (720 ft) but she could go as deep as 230–250 m (750–820 ft) without having her hull crushed. U-28's armament consisted of five 53.3 cm (21 in) torpedo tubes, (four located in the bow and one in the stern). She could have up to eleven torpedoes on board or 22 TMA mines or 33 TMB mines. U-28 was also equipped with a C35 88 mm gun/L45 deck gun with 220 rounds. Her anti-aircraft defenses consisted of one 2 cm (0.79 in) anti-aircraft gun.^[3]

First patrol

U-28's first war patrol took place from 19 August to 29 September 1939. On 14 September, while sailing around the mouth of St George's Channel, U-28 sank a 5,000 GRT freighter, which was her only success of the patrol.^[4]

Second patrol

U-28's second war patrol took place from 8 November to 12 December 1939. For this effort she was instructed to lay a minefield near the port city of Swansea. En route to Bristol, U-28 sank two ships; the 5,000 GRT Dutch tanker MV Sliedrecht and the 5,100 GRT British freighter SS Royston Grange. U-28 then laid her minefield and returned to port in Germany. While the minefield was not an immediate success, it sank the 9,600 GRT British freighter SS Protesilaus 60 days after it was laid.^[5]

Third patrol

U-28's third sortie took place from 18 February to 25 March 1940. She was instructed to lay mines off the British Naval Base at Portsmouth. After U-28 laid the minefield, she went on to sink two ships for 11,200 GRT.^[6]

Fourth patrol

U-28's fourth war patrol took place from 8 June to 7 July 1940. She was sent to the Western Approaches and turned in an average performance of sinking three ships totalling 10,300 GRT.^[7] The Irish government sought an explanation from Germany for the sinking of the neutral Greek ship Adamandios Georgandis: "the entire cargo of which comprised grain for exclusive consumption in Éire"^[8] She was sailing from Rosario (in Argentina) to Cork with a cargo of wheat when she was torpedoed and sunk^[9] south-west of Ireland at 43°35′N 11°15′W.

Fifth patrol

U-28's fifth war patrol took place from 11 August to 17 September 1940 and was one of Kuhnke's most productive. In August, she sank two ships for 5,500 GRT. On 10 September, U-28 found and tracked Convoy OA 210. In the darkness of early morning on 11 September, U-28 attacked the convoy and claimed two large freighters (13,000 GRT each) sunk and caused damage to a 10,000 GRT tanker, bringing Kuhnke's total for the patrol to five ships for 30,000 GRT. However, during the postwar analysis, he was only credited with sinking a 2,000 GRT Dutch freighter and damaging a 4,700 GRT British freighter; which, combined with his earlier sinkings, brought his total to four ships for 9,945 GRT. On his return to Lorient Kuhnke was awarded the Knight's Cross for his work.^[10]

Sixth patrol

U-28's sixth and final war patrol took her from Lorient back to Germany; because of the heavy seas and foul weather, U-28 sank only half a ship for 2,694 GRT. (U-28 and U-31 shared credit for the sinking of the SS Matina). On 15 November 1940, she returned to Germany and was turned over to the training command. Günter Kuhnke proceeded to command U-125.^[11]