Petty officer, 1st class, aka 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.
The rank insignia of the PO1 is a crown worn on both forearms of the Service Dress tunic, and on slip-ons on both shoulders of other uniforms. PO1s are generally initially addressed as "Petty Officer Bloggins" or "PO Bloggins", and thereafter as "PO", although in correspondence the full rank or abbreviation is used before the member's name. The full appellation "Petty Officer 1st-Class" or "PO1" in speech is generally used only when the "first-class" distinction be made, such as to distinguish between members with similar names but differing ranks, or on promotion parades.
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".