Master Chief Petty Officer is the ninth, and highest, enlisted rank (E-9) in the U.S. Navy and U.S. Coast Guard, just above
Senior Chief Petty Officer, and is a non-commissioned officer. They are referred to as Master Chief in most circumstances.
Advancement to Master Chief Petty Officer is similar to that of Chief Petty Officer and Senior Chief Petty Officer. It carries requirements of time in service, superior evaluation scores, specialty examinations, and peer review. A Senior Chief Petty Officer can only advance if a selection board of serving Master Chiefs approve, which is the same for First Class Petty Officers advancing to Chief Petty Officer, and Chief Petty Officers advancing to Senior Chief Petty Officer.
Like Petty Officers, every chief has both a rank and rating (job, similar to a Military Occupational Specialty (MOS) in other branches). A chief's full title is a combination of the two. Thus, a Master Chief Petty Officer, who has the rating of Fire Control Technician would properly be called a Master Chief Fire Control Technician.
Each rating has an official abbreviation, such as MM for Machinist's Mate, FT for Fire Control Technician, or STS for Sonar Technician Submarines. When combined with the petty officer level, this gives the short-hand for the chief's rank, such as FTCM for Master Chief Fire Control Technician. It is not uncommon practice to refer to the master chief by this short hand in all but the most formal correspondence (such as printing and inscription on awards). Mostly, though, they are simply called "Master Chief", regardless of rating.
The rate insignia for a master chief is a white eagle with spread wings above three chevrons. The chevrons are topped by a rocker that goes behind the eagle (or "crow", as it is commonly called). Two inverted silver stars (a reference to the stars used on the sleeves of line officers) are placed above the eagle. Between the rocker and the top chevron is the specialty mark of the enlisted rating the Master Chief is currently serving in. This is used on the Dress Blue uniform. On all other uniforms, the insignia used is the one that has become universally accepted as the symbol of the Chief Petty Officer. This is a fouled (entwined in the anchor chain) gold anchor superimposed with a silver "USN" in the Navy or a silver shield in the Coast Guard. Like the dress blue insignia, this is capped by two upside-down stars.
In the Navy, officers and chiefs are referred to as "khakis". This is a reference to the color of their most common uniforms, and is a direct contrast to those in paygrades E-6 and below (or "blueshirts"). In the Coast Guard, petty officers, chief petty officers, warrant officers, and commissioned officers all wear similar uniforms.
