The soldiers all used to do a six-month tour of duty in Northern Ireland.

士兵过去都要在北爱尔兰服役六个月。

《牛津词典》

The White House later claimed the banner was the Lincoln crew's idea, with a Pentagon spokesman saying it referred to the crew having just finished its tour of duty.

白宫随后声明这个标语是全体船员的想法，五角大楼发言人赞扬全体官兵圆满完成任务。

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We see those same qualities today, particularly in our young men and women in uniform who have served tour after tour of duty to defend our nation in harm’s way, and their civilian counterparts.

今天我们还可以看到美国人民的这些素质，尤其是穿着军装的年轻男女以及他们的文职伙伴，他们完成了一个又一个任务，为的就是保卫我们的国家免于危害。

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