ˌactive ˈservice BrE AmE ( also ˌactive ˈduty ) noun [uncountable]
the work that soldiers do in a war:
Powell was declared unfit for active service.
on active service/duty
More than 20,000 women are on active duty.
ACTIVE DUTY
Meaning of ACTIVE DUTY in English
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012