投军

投军	tóu jūn	to join up / to enlist (e.g. in the military)
投	tóu	to throw (sth in a specific direction: ball, javelin, grenade etc) / to cast (a ballot) / to cast (a glance, a shadow etc) / to put in (money for investment, a coin to operate a slot machine) / to send (a letter, a manuscript etc) / to throw oneself into (a river, a well etc to commit suicide) / to go to; to seek refuge; to place oneself into the hands of / (coll.) to rinse (clothes) in water
军	jūn	(bound form) army / military