For military soldiers, a tour of duty is usually a period of time spent in combat or in a hostile environment. For example, in World War II a tour of duty for a Royal Air Force (RAF) bomber crewman was 30 flights. That number could take up to 12 months.
In navies, a tour of duty is a period of time spent performing operational duties at sea, including combat, performing patrol or fleet duties, or assigned to service in a foreign country; a tour of duty is part of a rotation, where the ship may spend a six-month tour of duty, then spend one month in home port for maintenance, then a period of time on exercises, then return to her tour of duty.
A general tour of duty for soldiers comprises service that can last from half a year to four years. Generally, duties that last longer than two years are eligible to receive medals of merit related to their service. Tours of duty can also be extended involuntarily for service members, such as in September 2006 when the tour of duty was extended for 4,000 US military personnel in Iraq.