You can find records of officers' service in the Pay Lists and Muster Rolls.  These are found in the Catalogue; use the keywords muster books pay lists. Narrow your results (for example by year or country) using the right menu.

The Army Lists and Hart’s Army Lists may also provide details of army service, injuries and decorations.

Hart's Army List 1840 and Hart's Army List 1888 are also digitised and searchable in FindMyPast UK in eResources.

The Army Lists are  titled The Monthly Army List  and The Army Lists.