It shares many of the same rank structures and traditions with the US Navy, probably because it was something convenient that the writers could look at for a reference. Arguments about inconsistencies are somewhat valid in that regard, but in the end it is simply a creation of writing, which was produced by a large collection of people who didn't have the same knowledge or the same ideas on everything. For me such arguments about inconsistencies with regulations, traditions, or something else the modern military does simply make for interesting factoids to be taken worth a grain of salt as it applies to a fictional organization which exists in a fictional future.