In every branch of the US military the classifications are pretty straight forward and for the most part are self explanatory–except for the Navy–they don’t use the term ranks, their’s are referred to as rates. I’ve included the definition of rates per the US Navy below as well as some Navy rates that aren’t as self explanatory as others. I’ve left the link where I found the definitions if you’re interested in reading more on some that I don’t mention here. This was fun and I learned a few things, like if a Sailors mail is late he would go have a talk with the Yeoman.
The use of the word “rank” for Navy enlisted personnel is incorrect. The term is “rate.” The rating badge is a combination of rate (pay grade, as indicated by the chevrons) and rating (occupational specialty, as indicated by the symbol just above the chevrons).
The insignia here represents a Petty Officer First Class (the rate) who is a Boatswain’s Mate (the rating). A rating badge is worn on the left upper sleeve of all uniforms in grades E-4 through E-6. Chief Petty Officers (E-7 through E-9) wear collar devices on their white and khaki uniforms, and rating badges on their Service Dress Blues. (Source)
United States Navy ratings are general enlisted occupations that consist of specific skills and abilities. Each naval rating has its own specialty badge, which is worn on the left sleeve of the uniform by each enlisted person in that particular field. Working uniforms, such as camouflage Battle Dress Uniforms, utilities, coveralls, and Naval Working Uniform, bear generic rate designators that exclude the rating symbol.
Just as a naval officer has rank, not a rate, an officer’s occupation (if drawn more narrowly than an officer of the line) is classified according to designators for both officers of the line (e.g., line officers) and those of the professional staff corps.
Ratings should not be confused with rates, which describe the Navy’s enlisted pay-grades and ratings. Enlisted sailors are referred to by their rating and pay-grade. For example, if someone’s pay-grade is E-5 (Petty Officer 2nd Class) and his rating is Boatswain’s Mate, then combining the two—Boatswain’s Mate 2nd Class (BM2)—defines both pay-grade and rating in formal address or epistolary salutation. Thus, Boatswain’s Mate 2nd Class (BM2) would be his rate. A member that is E-1, E-2, or E-3 that belongs to a general occupational field (airman, constructionman, fireman, hospitalman, or seaman) is considered non rated. A striker is a nonrated person who is working for promotion towards a specific rating. Example: BMSN, MMFA, AOAR. (Source)
Boatswain’s Mate train and supervise personnel in all activities relating to marlinspike, deck, and boat seamanship, and oversee the maintenance of the ship’s external structure and deck equipment. They act as petty officers in charge of small craft and may perform duties as master-at-arms, serve in or take charge of gun crews, and damage control parties.
Boatswain’s Mates are also responsible for the “deck side” watch. In port three of the crew are on deck watch 24/7 (in hazardous areas such as war zones there are more than three, depending on ship’s size). They are the Officer of the Deck, Boatswain’s Mate of the watch, and Messenger of the Watch (usually a Seaman or Seaman Apprentice). They are stationed very close to the gangway and monitor all the comings and goings of persons to and from the ship. At sea the Boatswain’s Mate of the watch is within ear shot of the conning officer (on the bridge). The boatswain’s Mate of the watch supervises the rest of the enlisted watch standers on deck. They include helmsman, messenger of the watch, and all the look outs. In port or at sea the Boatswain’s Mate of the watch is charged with the responsibility of making all announcements to the crew; everything from chow call to general quarters (battle stations).
Aerographer’s Mate are the U.S. Navy’s weather forecasters. They are trained in meteorology and the use of aerological instruments that monitor air pressure, temperature, humidity, wind speed, and direction. They prepare weather maps and forecasts and can analyze atmospheric conditions to determine the best flight levels for aircraft. An AG can measure wind and air density to aid the accuracy of anti-aircraft firing, shore bombardment and delivery of weapons by aircraft.
Master-at-Arms uphold law and order aboard ships, shore stations, control access to naval installations, and deploy overseas with expeditionary forces and squadrons performing Antiterrorism/Force Protection (AT/FP) duties. The basic duty of an MA is to enforce rules and regulations, maintain good order and discipline, and protect life and property. Some other duties include conducting criminal investigations, personal protective services, take part in correctional and rehabilitative programs, Military Working Dog (MWD) handlers, small arms instruction, lethal and non-lethal weapons training, and organize and train sailors assigned to Shore Patrol police duty. Their equivalents in the civilian world are detectives, security guards, and policemen.
Quartermaster assist the navigator and officer of the deck (OOD), steer the ship, take radar bearings and ranges, make depth soundings and celestial observations, plot courses and command small craft.
Yeoman perform Administrative and Clerical work. They deal with visitors, coordinate worldwide travel, submit passport applications, telephone calls and incoming mail, and assist various ships, squadrons, staff commands, and special warfare teams around the world with administrative tasks. They write and type business and social letters, notices, directives, forms and reports.
Signalman Disestablished on 4 November 2003 and duties absorbed by Quartermaster rating. Signalman was a U.S. Navy rating for sailors that specialized in visual communication. See Signaller for more about the roles of Signalmen. (Source)
Petty officer The modern petty officer dates back to the Age of Sail. Petty officers rank between naval officers (bothcommissioned 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. (Source)