Master chief petty officer, or MCPO, or master chief, is the ninth enlisted rank and is the second-highest non-commissioned officer rank in Starfleet. It is senior to the rank of senior chief petty officer and junior only to the Master Chief Petty Officer of Starfleet.
Advancement to the rank of master chief petty officer is similar to that of chief petty officer and senior chief petty officer. It carries requirements of time served in Starfleet, superior evaluation scores, specialty examinations, and a review of peers. A senior chief can advance to master chief only if a selection board of serving MCPOs approves, which is the same for petty officers first class advancing to the rank of chief petty officer, and chief petty officers advancing to senior chief.
Master chief petty officers are generally considered to be technical experts in their fields. As such they are normally assigned to major fleet commands and fleet staffs. Many MCPOs choose to enter the Command Master Chief Petty Officer Program. If selected they receive additional leadership training and may be assigned to commands as the command master chief (CMC). The command master chief petty officer is the senior enlisted person at a command and as such works as a liaison between the commanding officer and the enlisted ranks within that command, being referred to as the chief of the boat or COB for short. In this capacity the CMC assists both the commanding officer and the first officer in issues of quality of life, discipline, training, and morale. The same applies for a fleet master chief petty officer, who acts as a liaison between the fleet's commander and the fleet's noncoms.
Rank insignia of Starfleet master chief petty officers