While the Navy is fine with Reynolds playing, he must receive final approval from the U.S. Secretary of Defense Ash Carter for the clearance to become official. According to Ravens' official website, Mabus "strongly recommended" in his request to the Secretary of Defense that Reynolds be granted permission to play.
Athletes from the Navy, Army and Air Force academies are required to complete active duty military service following graduation, which is why permission is required. According to the academy's official site, the Navy requires five years in exchange for tuition, room and board, medical and dental care costs.
Last year, Reynolds broke the NCAA career record for touchdowns scored (88 rushing/receiving and 31 passing), though he'll likely find a place as a running back or wideout in Baltimore.
He joins the roster at an interesting time. Reynolds is no doubt an explosive athlete and Baltimore's offense is trying to make up for a season where their skill position players seemed stuck in neutral. The team signed former top-five pick Trent Richardson to add some competition to their backfield. At wide receiver, Reynolds will have to compete against the likes of Breshad Perriman, Marlon Brown and Chris Moore for playing time. Kamar Aiken, Steve Smith and Mike Wallace appear to be the likely starters.