U-28 was commissioned into the Imperial German Navy on 26 June 1914, with Freiherr Georg-Günther von Forstner (1882-1940) in command.Commander von Forstner was relieved on 15 June 1916 by Otto Rohrbeck, who was in turn relieved on 5 August by Freiherr von Loe-Degenhart. On 15 January 1917, Georg Schmidt took command.
On 30 July 1915, U-28 sank the British steamer Iberian. According to Commander von Forstner's account of the incident, the wreckage remained under the water for about 25 seconds until an explosion sent some of the debris flying up. It is said that along with the debris, a creature described as a "gigantic aquatic animal" resembling a crocodile was seen, which quickly disappeared from sight.[1]
U-28s final patrol began on 19 August 1917, when it departed from Emden for the Arctic Ocean. On 2 September, at 11:55 am, it encountered the armed English steamer, north-by-northeast of North Cape, Norway. U-28 scored a torpedo hit, and closed in to finish the steamer with gunfire. The shells detonated Olive Branchs cargo of munitions, which it had been carrying from England to Arkhangelsk, Russia, and the subsequent explosion so badly damaged the nearby U-boat that it sank along with the steamer. All 39 of its crew were lost; some were seen swimming, but were not picked up by Olive Branchs lifeboats.[2]
An alternative description of the event states that when the ammunition detonated, a truck carried as deck cargo was blown into the air and fell from a great height on the U-boat, sinking it.[3]
| Date | Name | Nationality | Tonnage | Fate[4] | |
|---|---|---|---|---|---|
| 17 March 1915 | Leeuwarden |  United Kingdom | 990 | Sunk | |
| 18 March 1915 | Zaanstrom |  Netherlands | 1,657 | Captured as prize | |
| 18 March 1915 | Batavier V | Netherlands | 1,569 | Captured as prize | |
| 25 March 1915 | Medea | Netherlands | 1,235 | Sunk | |
| 27 March 1915 | United Kingdom | 2,114 | Sunk | ||
| 27 March 1915 | South Point | United Kingdom | 3,837 | Sunk | |
| 27 March 1915 | Vosges | United Kingdom | 1,295 | Sunk | |
| 28 March 1915 | United Kingdom | 4,806 | Sunk | ||
| 28 March 1915 | City Of Cambridge | United Kingdom | 3,788 | Damaged | |
| 29 March 1915 | Flaminian | United Kingdom | 3,500 | Sunk | |
| 29 March 1915 | Theseus | United Kingdom | 6,723 | Damaged | |
| 30 March 1915 | Crown of Castile | United Kingdom | 4,505 | Sunk | |
| 30 July 1915 | Iberian | United Kingdom | 5,223 | Sunk | |
| 31 July 1915 | Nugget | United Kingdom | 405 | Sunk | |
| 31 July 1915 | Turquoise | United Kingdom | 486 | Sunk | |
| 1 August 1915 | Benvorlich | United Kingdom | 3,381 | Sunk | |
| 1 August 1915 | Clintonia | United Kingdom | 3,830 | Sunk | |
| 1 August 1915 | Koophandel |  Belgium | 1,736 | Sunk | |
| 1 August 1915 | Ranza | United Kingdom | 2,320 | Sunk | |
| 2 August 1915 | HMS Portia | 494 | Sunk | ||
| 3 August 1915 | Costello | United Kingdom | 1,591 | Sunk | |
| 4 August 1915 | Midland Queen |  Canada | 1,993 | Sunk | |
| 26 March 1916 | Norne |  Norway | 1,224 | Sunk | |
| 28 March 1916 | Rio Tiete | United Kingdom | 3,042 | Sunk | |
| 30 March 1916 | Trewyn | United Kingdom | 3,084 | Sunk | |
| 30 March 1916 | Saint Hubert |  France | 232 | Sunk | |
| 31 March 1916 | Vigo |  | 1,137 | Sunk | |
| 1 April 1916 | Bengairn | United Kingdom | 2,127 | Sunk | |
| 29 May 1917 | Fridtjof Nansen | Norway | 2,190 | Sunk | |
| 29 May 1917 | Karna | Norway | 210 | Sunk | |
| 29 May 1917 | Kodan | Norway | 217 | Sunk | |
| 3 June 1917 | Merioneth | United Kingdom | 3,004 | Sunk | |
| 4 June 1917 | Algol | 2,088 | Sunk | ||
| 5 June 1917 | Alaska | Norway | 90 | Sunk | |
| 5 June 1917 | Duen | Norway | 30 | Sunk | |
| 5 June 1917 | Sydkap | Norway | 40 | Sunk | |
| 8 June 1917 | Manchester Engineer | United Kingdom | 4,465 | Damaged | |
| 8 June 1917 | Sverre II | Norway | 44 | Sunk | |
| 10 June 1917 | Marie Elsie | United Kingdom | 2,615 | Sunk | |
| 10 June 1917 | Perla | United Kingdom | 5,355 | Sunk | |
| 28 August 1917 | Hidalgo | United Kingdom | 4,271 | Sunk | |
| 28 August 1917 | Whitecourt | United Kingdom | 3,680 | Sunk | |
| 28 August 1917 | Marselieza | 3,568 | Sunk | ||
| 1 September 1917 | Dront | 3,488 | Sunk | ||
| 2 September 1917 | Olive Branch | United Kingdom | 4,649 | Sunk |