The OSM was introduced in 2000 superseding the General Service Medal 1962 (with the exception of the GSM with NORTHERN IRELAND clasp).
Three separate OSMs have been issued and each has a different ribbon to denote service in:
- Sierra Leone (OP PALLISER, BASILICA, SILKMAN, MAIDENLY*, BARRAS*)
- Afghanistan (OP HERRICK)
- Democratic Republic of the Congo (OP CORAL).
*A silver rosette may be awarded for OP MAIDENLY and OP BARRAS to be worn on the Sierra Leone OSM to signify service in a more dangerous area/period of conflict.