Nummer: 15703
| Area : | Western Area |
| Sea area : | North Atlantic |
| Date of attack : | 13.03.1943 |
| Time of attack : | 23:22 |
| Nationality of U-boat : | German |
| U-boat : | U 172 |
| Commander : | Emmermann |
| Grid : | CD 6823 |
| presumed target type : | Steam Freighter id |
| presumed tonnage : | 5565 BRT |
| presumed result : | sunk |
| Used weapon(s) : | Torpedo(es) |
| Convoy : | UGS.6 |
| Date of observation : | 13.03.1943 |
| Nationality of target : | American |
| Actual type of target : | Steam Freighter |
| Name of target : | Keystone |
| Year of launch : | 1919 |
| Actual tonnage : | 5565 BRT |
| Actual result : | sunk |
| Position of target : | 37.59n 37.40w |
| Footnote : | U-172 reported the old name of "Keystone" ex "Sage Brush". |
Steam Freighter Keystone ex American Sage Brush (bis 1941)
| Convoy : | UGS.6 |
| Route of convoy : | U.S.A. - Gibraltar (slow) |
| Remark to convoy : | Since Oct 1942, initially for Op. Torch, then to ports in Northwest-Africa |