Nummer: 28403
| Area : | Pacific Ocean |
| Sea area : | South Pacific |
| Date of attack : | 31.08.1943 |
| Nationality of U-boat : | Japanese |
| U-boat : | I-20 |
| Commander : | Otsuka |
| Grid : | New Hebrides |
| presumed target type : | Tanker |
| presumed result : | sunk |
| Used weapon(s) : | Torpedo(es) |
| Date of observation : | 31.08.1943 |
| Time of observation : | 15:35 |
| Nationality of target : | American |
| Actual type of target : | Steam Tanker |
| Name of target : | W.S. Rheem |
| Year of launch : | 1911 |
| Actual tonnage : | 10872 BRT |
| Actual result : | damaged |
| Position of target : | 15.51s 167.02e |