These AN (Army/Navy) equipment indicators are built of the "AN" prefix, a slash, and then the three-letter descriptors.

Example: AN/MPN-14: Ground, mobile, radar, navigational aid (the kind I worked on in the U.S. Air Force).

     AN = Army/Navy
       M = Ground Mobile
       P = Radar
       N = Navigational Aid
    -14 = Number in the series
 
Refer to AN Component Designators for replacements to the AN indicator.

1st Letter Designated Installation Classes	2nd Letter Type Of Equipment	3rd Letter Purpose
A - Airborne (installed and operated in aircraft)	A - Invisible light, heat radiation	A - Auxiliary assemblies (not complete operating sets used with, or part of, two or more sets or sets series
B - Underwater mobile, submarine	B - Pigeon	B - Bombing
C - Air transportable (inactivated, do not use)	C - Carrier	C - Communications (receiving and transmitting
D - Pilotless Carrier	D - Radiac	D - Direction finder, reconnaissance, and/or surveillance
	E - Nupac	E - Ejection and/or release
F - Fixed	F - Photographic
G - Ground, general ground use (include two or more ground-type installations)	G - Telegraph or teletype	G - Fire-control or searchlight directing
		H - Recording and/or reproducing (graphic meteorological and sound
	I - Interphone and public address
	J - Electromechanical or inertial wire covered
K - Amphibious	K - Telemetering	K - Computing
	L - Countermeasures	L - Searchlight control (Inactivated, use G)
M - Ground, mobile (installed as operating unit in a vehicle which has no function other than transporting the equipment)	M - Meteorological	M - Maintenance and test assemblies (including tools)
	N - Sound in air	N - Navigational aids (including altimeters, beacons, compasses, rapcons, depth sounding, approach and landing
P - Pack or portable (animal or man)	P - Radar	P - Reproducing (inactivated, do not use)
	Q - Sonar and underwater sound	Q - Special, or combination of purposes
	R - Radio	R - Receiving, passive detecting
S - Water surface craft	S - Special types, magnetic, etc., or combinations of types	S - Detecting and/or range and bearing, search
T - Ground, transportable	T - Telephone wire	T - Transmitting
U - General utility (includes two or more general installation classes, airborne, shipboard, and ground)
V - Ground, vehicular (installed in vehicle designed for functions other than carrying electronic equipment, etc., such as tanks)	V - Visual and visible light
W - Water surface and underwater	W - Armament (peculiar to armament, not otherwise covered)	W - Automatic flight or remote control
	X - Facsimile or television	X - Identification and recognition
	Y - Data processing