join up
1．offer oneself as a recruit；join the army 参军；入伍
He joined up at the age of twenty．他20岁参了军。
On leaving collage，my brother joined up．我的兄弟大学毕业后参军了。
2．connect；link together 连接
The electrician joined the wires up．电工把电线接好了。
3．form or enter into an alliance or league；link up 组成或参加联盟；会合
The two companies were ordered to join up with each other at Bridge No．3 before dawn．那两个连奉命于黎明前在3号桥会师。