active duty
noun (especially North American English)(also active service especially in British English)
[uncountable]taking part in military action as a member of the armed forces 现役：以武装部队成员的身份参加军事行动 He has been treated in hospital and is returning to active duty. 他已在医院接受治疗，正在恢复服役。 - on active duty
He sustained serious injuries while on active duty. 他在服役期间受了重伤。