German submarine U-28 was a Type VIIA U-boat of Nazi Germany's Kriegsmarine during World War II.
Her keel was laid down on 2 December 1935, by DeSchiMAG AG Weser of Bremen. She was launched on 14 July 1936, and commissioned into Kriegsmarine on 12 September 1936, with Kapitänleutnant Wilhelm Ambrosius in command. Ambrosius was succeeded by nine other commanding officers over the next eight years.
Second patrol
U-28s second war patrol took place from 8 November to 12 December 1939. She was tasked with laying a minefield near the port city of Swansea. En route to Bristol, U-28 sank two ships: the Dutch tanker and the 5,100 GRT British freighter 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 Protesilaus 60 days after it was laid.
Third patrol
U-28s 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 laying the minefield, she went on to sink two ships for 11,200 GRT.
Fourth patrol
U-28s 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. 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". She had been sailing from Rosario, Argentina to Cork with a cargo of wheat when she was torpedoed and sunk south-west of Ireland at .
Fifth patrol
U-28s 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 early morning darkness of 11 September, U-28 attacked the convoy, claiming two large freighters (13,000 GRT each) sunk and one 10,000 GRT tanker damaged, 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, France, Kuhnke was awarded the Knight's Cross for his work.
Sixth patrol
U-28s sixth and final war patrol took her from Lorient back to Germany. Hampered by heavy seas and foul weather, U-28 sank only half a ship for 2,694 GRT.; U-28 and 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 .
Fate
U-28 sank by accident on 17 March 1944, at the U-boat pier in Neustadt, Germany. During a training exercise, the boat had passed under a dummy freighter used for target practice. The commander-in-training failed to note the position of the stationary freighter, and the U-boat's conning tower was ripped off. Water flooded the control room, but the other compartments remained intact. The crew escaped by slowly equalizing the water pressure in the boat and swimming to the surface. The boat was raised in March 1944, but was stricken on 4 August. The submarine's crew suffered no casualties during her career.||Fate
|-
| align="right"|14 September 1939
| align="left" |Vancouver City
| align="left" |
| align="right"|4,955
| align="left" |Sunk
|-
| align="right"|17 November 1939
| align="left" |
| align="left" |
| align="right"|5,133
| align="left" |Sunk
|-
| align="right"|25 November 1939
| align="left" |Royston Grange
| align="left" |
| align="right"|5,144
| align="left" |Sunk
|-
| align="right"|21 January 1940
| align="left" |Protesilaus
| align="left" |
| align="right"|9,577
| align="left" |Total loss (mine)
|-
| align="right"|9 March 1940
| align="left" |P. Margoronis
| align="left" |
| align="right"|4,979
| align="left" |Sunk
|-
| align="right"|11 March 1940
| align="left" |Eulota
| align="left" |
| align="right"|6,236
| align="left" |Sunk
|-
| align="right"|18 June 1940
| align="left" |Samartia
| align="left" |
| align="right"|2,417
| align="left" |Sunk
|-
| align="right"|19 June 1940
| align="left" |Adamandios Georgandis
| align="left" |
| align="right"|3,443
| align="left" |Sunk
|-
| align="right"|21 June 1940
| align="left" |HMS Prunella
| align="left" |
| align="right"|4,443
| align="left" |Sunk
|-
| align="right"|27 August 1940
| align="left" |Eva
| align="left" |
| align="right"|1,599
| align="left" |Sunk
|-
| align="right"|28 August 1940
| align="left" |Kyno
| align="left" |
| align="right"|3,946
| align="left" |Sunk
|-
| align="right"|9 September 1940
| align="left" |Mardinian
| align="left" |
| align="right"|2,434
| align="left" |Sunk
|-
| align="right"|11 September 1940
| align="left" |Harpenden
| align="left" |
| align="right"|4,678
| align="left" |Damaged
|-
| align="right"|11 September 1940
| align="left" |Maas
| align="left" |
| align="right"|1,966
| align="left" |Sunk
|-
| align="right"|26 October 1940
| align="left" |Matina
| align="left" |
| align="right"|5,389
| align="left" |Damaged
|}