The uniform with the flap on the back use to be the work uniform in the days of yore, which explains perfectly why it is now the dress uniform. To keep it as uniform as possible, this uniform comes in two colors, blue--which is really black but don't tell any one, and white. Now, since we don't want to confuse the sailors both of these uniforms are worn with white dixie cup hats and black shoes---these uniforms are nicknamed "cracker jacks" on account of the cracker jack guy is the most famous sailor to wear them. Okay, so, since the work uniform is now the dress uniform, we needed to create a work uniform. This work uniform, which is worn by all junior enlisted, unless that junior enlisted is actually going to do work in which case he or she will wear the dungaree uniform or the cover-all uniform--here we don't care about confusing the sailor so those two working uniforms can be worn with ball caps, hard hats or dixie cups--okay but I digress-so back to the non-working working uniform--this is a blue (black) uniform the shirt buttoning down the front worn with a tie and black slacks and black shoes--unless you are a woman in which case the uniform can be a skirt (obviously designed by a man) and can be worn with the uniform shoes for a skirt, which are either a stylish little pump (designed by a man) or a matronly flat (designed by someone who had to wear them) BUT NOT the uniform shoes that are worn with the female slacks. Now this uniform is worn with a garrison cap nicknamed a "piss cutter", unless you are a woman then your unifrom can be worn with a beret, and the whole uniform is nicknamed "gunfighters" because, well you look like the bad guy in a spaghetti western. Gun fighters can also be worn by Chief Petty Officers and Officers, but they wear white hats with black brims called "combination covers" Combination covers are only white and are worn with both black--err, blue--and white uniforms. Okay, gunfighters can be worn with three different uniform jackets, the Eisenhower, The reefer (pea coat) or the trench coat (flasher) all perfectly useless at keeping you warm. Officers have a fourth uniform option which is the $600 bridge coat which is worth the money because it keeps you warm and picks up chicks.
That seems perfectly intuitively obvious to me---