措手不及
[词典] (事情来得太快, 出乎意外, 来不及应付) be taken by surprise; be caught unawares [unprepared]; be too late to do anything about it; be too surprised to defend oneself; unaware;
[例句]我们打了它个措手不及,一枪没放就把他们收拾掉了。
Our enemies were caught unprepared and we disposed of them without firing a single shot.
unaware
unprepared
.