1. 指“军队”，既指“军队”的'总称，也侧重指“陆军”。比较：navy 海军 / air force 空军
2. 用作主语，谓语动词用单数 或复数 均可：
The army was [were] wiped out. 这支军队被消灭了。
3. “参军”及相关说法有两类，请注意区别：
join the army / go into the army / become a soldier / enter the army：它们均为终止性动词，不能与一段时间连用。
be in the army / be a soldier：均说明状态，可与一段时间连用。
他参军10年了。
正：He joined [went into] the army ten years ago.
正：He has been in the army for ten years.
正：He has been a soldier for ten years.
误：He joined [went into] the army for ten years.