tour of duty
noun /ˌtʊər əv ˈdjuːti/,  /ˌtɔːr əv ˈdjuːti/
  /ˌtʊr əv ˈduːti/
(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
- She has served two tours of duty overseas.
 - They have recently returned from a year-long tour of duty.
 - on a tour of duty He was wounded while on a tour of duty.