The modern petty officer dates back to the Age of Sail. Petty officers rank between naval officers and most enlisted sailors. These were men with some claim to officer rank, sufficient to distinguish them from ordinary ratings, without raising them so high as the sea officers. Several were warrant officers, in the literal sense of being appointed by warrant, and like the warrant sea officers, their superiors, they were usually among the specialists of the ship's company. The Oxford English Dictionary suggests that the title derives from the Anglo-Norman and Middle French "petit", meaning "of small size, small, little". Two of the petty officer's rates, midshipman and master's mate, were a superior petty officer with a more general authority, but they remained no more than ratings. However, it was quite possible for a warrant officer, in his role as a superior officer, to be court-martialed for striking a midshipman. This is because both were regarded as future sea officers, with the all-important social distinction of having the right to walk the quarterdeck. Midshipmen wore distinctive uniforms, master's mates dressed respectably, and both behaved like officers. The master's mate rating evolved into the rank of sub-lieutenant, and midshipman evolved into naval cadet.
Usage in navies
Canada
There are two petty officer ranks in the Royal Canadian Navy. Petty officer, 2nd class is equivalent to a sergeant and petty officer, 1st class is equivalent to a warrant officer. Petty officers are normally addressed as "Petty Officer Bloggins" or "PO Bloggins", thereafter as "PO". The "1st class" and "2nd class" designations are normally only used when such a distinction needs to be made, such as on a promotion parade or to distinguish two petty officers with similar names but different ranks. The NATO rank denotion for "petty officer, 2nd class" is OR-6. The NATO rank denotion for "petty officer, 1st class" is OR-7.
India
A petty officer is a non-commissioned officer in the Indian Navy, equivalent to the NATO rank enlisted grade of OR-5. They are equal in rank to a sub inspector of police in the Indian Police Services, or sergeant in the Indian Army and Indian Air Force. A petty officer is superior in rank to a leading rate and subordinate to a chief petty officer, as is the case in the majority of Commonwealth navies. A petty officer has the ability to work as a leader, capable of taking charge of a group of personnel, and taking roles in the training and recruitment of new members of the Indian Navy.
In some countries the same term is used as for a non-commissioned officer in land forces, e.g. "suboficial" in some Spanish-speaking countries. The Russian equivalent is Glavny Starshina.