Petty officer
A petty officer (PO) is a non-commissioned officer in many navies and is given the NATO rank denotion OR-6. They are equal in rank to sergeant in the British Army and Royal Air Force. A petty officer is superior in rank to leading rate and subordinate to chief petty officer, in the case of the British armed forces.
The modern petty officer dates back to the Age of Sail. Petty officers rank between naval officers (both commissioned and warrant) 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 ships'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 (such as the armourer), 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.
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