Enlistment
Enlist
noun, verbal noun
Entering into a squad is called enlistment!
入隊 can refer to enlisting in any group that ends with 隊 (squad), like the 軍隊 (military) or an 音楽隊 (marching band). These are indeed the most common uses.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
ついに音楽隊への入隊が決まりました。
I finally decided to join the band.
入隊試験に面接があるとは思ってもみなかった。
I never thought there would be an interview for the enlistment test.
日本人男性がアメリカ軍に入隊することはできますか。
Can a Japanese man enlist in the U.S. military?