What rank is CM2 in the US Naval Reserve?

A CM 2 is a Construction Mechanic - the CM is for the rate designation, the 2 is for the Petty Officer (NCO) rank level, which in this case is a Petty Officer 2nd Class. The enlisted pay rate is E-5.

CM's are responsible for repairing and maintaining heavy construction equipment of all types (bulldozers, dump trucks, etc.). They are one of several rates that comprise the Navy's Construction Battalion (SeaBees) force.