They setoff, two men out in front as scouts, two behind in case of any attack from the rear.
他们出发了，两人在前作为侦察员，两人殿后以防后方攻击。
《柯林斯英汉双解大词典》
2
Xerox set about a process of reverse engineering. It pulled the machines apart and investigated the Japanese factories to find out how they could pull off such feats.