Petty officer, 1st class, PO1, is a Naval non-commissioned member rank of the Canadian Forces. It is senior to the rank of petty officer 2nd-class and its equivalents, and junior to chief petty officer 2nd-class and its equivalents. Its Army and Air Force equivalent is warrant officer (WO). The French form of the rank is maître de 1re classe. PO1s generally mess and billet with chief petty officers and other petty officers, and their army and air-force equivalents, warrant officers and sergeants. Their mess on a naval base or installation is generally named the "Chiefs and POs Mess".