tour of duty
noun(also tour)
(plural tours of duty)
a period of time when somebody is serving in the armed forces or as a diplomat in a particular place 出差旅行：某人在武装部队中服役或在特定地方担任外交官的时期 She has served two tours of duty overseas. 她已经在海外服过两次兵役。 They have recently returned from a year-long tour of duty. 他们最近结束了一年的服役期回来了。 - on a tour of duty
He was wounded while on a tour of duty. 他在执行任务时受伤了。