The following designations and their abbreviations have been used by Marine helicopter squadrons. For those not familiar with this system, the first letter, either V for fixed-wing, or H for helicopter indicates type of aircraft flown. This is followed by one or more letters to indicate the type of squadron. Marine squadrons add an M following the type designation. (HT= Helicopter Training Squadron (Navy); HMT=Marine Helicopter Training Squadron).
HMA Marine Attack Helicopter Squadron (1971 - 86)
HMH Marine Heavy Helicopter Squadron (1962 - present)
HMHT Marine Heavy Helicopter Training Squadron (1966 - 1972)
HML Marine Light Helicopter Squadron (1968 - 1994)
HMLA Marine Light Attack Helicopter Squadron (1983 - present)
-- Note: The two East Coast squadrons (167 and 269) insist on the non-standard "HML/A" designation.
HMM Marine Medium Helicopter Squadron (1962 - present)
HMMT Marine Medium Helicopter Training Squadron (1966 - 72/1999 - present)
HMO Marine Helicopter Observation Squadron (not used) This was the proposed designation for the Marine Observation Squadrons when they switched from fixed-wing operations to helicopters in the 1950s. This change never occured.
HMR Marine Helicopter Transport Squadron (1951 - 62)
HMR(C) Marine Helicopter Transport Squadron (Composite)(1956 - 58) Only 3 squadrons were so designated and were used in the reconaissance role. Not used by Reserves.
HMR(L) Marine Helicopter Transport Squadron (Light)(1956 - 62). Designation was not used by Reserves.
HMR(M) Marine Helicopter Transport Squadron (Medium) (1957 - 62). Not used by Reserves.
HMX Marine Helicopter Squadron (1947 - present).
VMM Marine Medium Tiltrotor Squadron (2006 - present).
VMMT Marine Medium Tiltrotor Training Squadron (1999 - present). 1 squadron.
VMO Marine Observation Squadron (1943 - 1994). Helicopter use began in 1950 and ended in 1972.
VMX Marine Tilt-Rotor Test and Evaluation Squadron (2003 - present). 1 squadron.