MACOs have similar training and tactics as the special forces of a number of member nations of United Earth (the US Navy SEALS, Delta Force, Army Rangers, Marine Force Recon, Special Air Service, etc), and their rank insignia is similar to that of the U.S. Marine Corps. Their operation aboard Starfleet vessels is comparable to that of the U.S. Marines on board U.S. Navy vessels in the 20th and 21st centuries.