Use of the term "commodore" dates from 1775 in the then–Continental Navy,
Today, it is no longer a specific rank within Active Duty or Reserve ranks, but it continues to be used as an honorary title within the U.S. Navy and the U.S. Coast Guard for those senior captains (pay grade O-6) in command of operational organizations composed of multiple independent subordinate naval units (e.g., multiple independent ships or aviation squadrons).
https://en.wikipedia.org/wiki/Commodore_(United_States)#Early_days