防备敌人突然袭击

be prepared for surprise attacks by the enemy

部队一直处于警戒状态以防突然袭击。

The Armies were constantly on the alert not to be taken by surprise.

他们一直处于常备不懈状态以防突然袭击。

They were constantly on the alert not to be taken by surprise.

我们的突然袭击把敌人打了个冷不防，他们顿时乱作一团。

Our surprise attack caught the enemy off balance and threw them into confusion.