(M) – Medical Officer

MAAF – Mediterranean Allied Forces / Malayan Auxiliary Air Force
MAC – Mediterranean Air Command
MACAF – Mediterranean Allied Coastal Air Force
MACP – Medic Air Command Post
MAD – Marine Acceptance Depot
MAED – Marine Aircraft Experimental Depot
MAEE – Marine Aircraft Experimental Establishment
MAEOp – Master Electronics Operator

"Mae West" – Life-saving vest, which can be inflate if the wearer falls into the water

MAEU – Marine Aircraft Experimental Unit
MAFIS – Midlands Area Flying Instructors School
MALM – Master Air Load-Master

MAMS - Mobile Air Movements Squadron

MAP – Ministry of Aircraft Production
MAREL – Moveable Air Reconnaissance Exploitation Unit
MASAF – Mediterranean Allied Strategic Air Force

MASFS – Midlands area School of Special Flying
MASR&CF – Malta Air Sea Rescue & Communications Flight
MATAF – Mediterranean Allied Tactical Air Forces
MBE – Member (of the Order of the) British Empire

MBF – Mobile Balloon Flight

(Mc) – Marine Craft Officer

MC – Military Cross (medal)
MCA – Ministry of Civil Aviation
MCC&FF – Maintenance Command Communication and Ferry Flight

MCCS/F – Maintenance Command Communications
MCJTF – Maintenance Command Jet Training Flight
MCRS – Marine Craft Repair Section

MCS – Metropolitan Communication Squadron
MC&TTS – Malta Communication & Target Towing Flight
MCTC – Military Corrective Training Centre

MCTS – Marine Craft Training Centre

MCU – Mosquito Conversion Unit / Meteorological Conversion Unit
Me – Messerschmitt
ME – Middle East
MEAC – Middle East Air Command
MEAF – Middle East Air Force

MEAS – Middle East Armament School
MEAFITF – Middle East Air Force Instrument Training Flight
MEAFTTU – Middle East Air Force Target Towing Unit

(L) – Legal Branch Officer

LAAGS – Light Anti–Aircraft Gunnery School
LAAPC – Light Anti–Aircraft Practice Camp
LAC – Leading Aircraftman
LACW – Leading Aircraft woman
LAS – Light Aircraft School
"(to) Lay on" – To arrange or produce anything

LCF – Lincoln Conversion Flight

"Left, right and center" – All over the place
LFS – Lancaster Finishing School
LG – Landing Ground

LGSM – Long Service and Good Conduct Medal
LLF – Light Liaison Flight
LLTU – Leigh Light Training Unit
LNSF – Light Night Striking Force, of Mosquitoes of 8 Group
LRFG – Long Rang Desert Group
LRFU – Long Rang Ferry Unit
LRDF – Long Range Development Flight
LRDU – Long Range Development Unit
LRWRE – Long Range Weapons Research Establishment
LTW – Lyneham Transport Wing
LRWE – Long Range Weapons Research Establishment

MEAS – Middle East Armament School

MEC – Middle East Command
MECGS – Middle East Central Gunnery School
MedMe – Mediterranean and Middle East
MEF – Middle East Forces
MEFC – Middle East Ferry Control
MENVTS – Middle East Night Vision Training School
MEP&AP – Middle East Pilot & Aircrew Pool
Met – Meteorological

Met Res – Meteorological Research
METS – Middle East Training School
MFH – Mobile Field Hospital

MFNU – Malta Night Fighter Unit
MFPU – Mobile Field Photographic Unit
MGSP – Mobile Glider Servicing Party
"Mickey Mouse" – Bomb dropping mechanism

Min Tech – Ministry of Technology

MiD – Mentioned in Dispatches
Mk – Mark
MMESTF/S – Mediterranean& Middle East Special Transport Flight/Squadron
MO – Medical Officer
MOA – Ministry of Aviation
MOD – Ministry of Defence
MOD(PE) Ministry of Defence (Procurement Executive)
MORU – Mobile Operations Room Unit
MOS – Marine Observation School
MoS – Ministry of Supply
MOTU – Marine Operational Training Unit
MRAF – Marshal of the Royal Air Force

MRES – Missing Research and Enquiry Service
MRF – Meteorological Research Flight
MRS – Maritime Reconnaissance School
MR squadron – Medium Reconnaissance squadron
MRT – Mountain Rescue Team

MSFU – Merchant Ship Fighter Unit
MSR –– Morse Slip Reader
MSU – Maintenance Sub Unit
MT – Mechanical Transport
MTD – Mechanical Transport Driver
MTLRU – Mechanical Transport Light Repair Unit

MTMS – Mechanical Transport Maintenance Section
MTU – Mosquito Training Unit
MU – Maintenance Unit
MUG – Mid Upper Gunner

MV – Merchant Vessel