When I joined the Navy, ... (Para. 11)
Meaning: When I became a member of the Navy, ... . More examples:
He joined the Labour Party when he left the university. 他离开大学后加入了工党。
He joined the army without first getting permission from his parents. 他在未征求父母同意的情况下参了军。
When "join" means "take part in some activity", the verb should be used with "in". Look at the following examples:
We all joined in the singing. 我们一起唱起了歌。
Will all of you join with me in drinking a toast to the success of this business! 请诸位和我一起为企业的成功干杯!