Nummer: 17309
| Area : | Western Area |
| Sea area : | North Atlantic |
| Date of attack : | 17.10.1943 |
| Time of attack : | 05:29 |
| Nationality of U-boat : | German |
| U-boat : | U 309 |
| Commander : | Mahrholz |
| Grid : | AK 3558 |
| presumed target type : | Steam Freighter |
| presumed result : | damaged |
| Used weapon(s) : | Torpedo(es) |
| Convoy : | ONS.20 |
| Actual tonnage : | ---- -- |
| Actual result : | hit not ascertained |
| Footnote : | U-309 fired a 3-torpedo spread and heard two FAT detonations after 13 min, probably end-of-run detonations. |
| Convoy : | ONS.20 |
| Route of convoy : | United Kingdom - North America (slow) |
| Remark to convoy : | 2nd series: Apr 1943 with new numbering (counter traffic SC) |