Here's a recap of all we know collectively about Fairchild M- designations.
Model 45 US Navy JK-1 utility transport (45-A: Argentina export variant)
Model 46 F-46 (also known as the Clark GA-46)
Model 47 F-47
M-62 tandem-seat trainer / A: PT-19 CORNELL / A-3: Ranger 6-440-C5
M-62B designation F-62B found, could indicate a projected civilian version
M-62C PT-23 CORNELL (also a strange M-62CF-23B designation found)[/i]
M-77 XAT-13/-14 "YANKEE DOODLE"/BOMBARDIER
M-78 XC-82 PACKET
M-79 XBQ-3
M-80 80/-1/-2 AT-21 GUNNER
M-82 4-place low-wing cabin proposal (1943)
M-84 civil 4-place PT conversion, single engine (M-84A/C) (1944)
M-85 twin-engine fighter project with 2 x Ranger SGV-770-D-4B engines (1944)
M-90 90-F feederline airplane tractor proposal (1944)
M-92 US Navy XNQ-1 trainer
M-95 centerline thrust feederline airplane (1945)
M-99 heavy cargo project with 4 x T35-1 turbines
M-103 USN 5-place aircraft developed from XNQ-1 (-103: R-985B-5, -103A: Fairchild Ranger SGV-770C-2C)
M-104 track gear installation retrofitted on C-82A (c/n 10116, USAAF s/n 45-57746)
M-105 XC-119A FLYING BOXCAR (XC-82B) (M-105A)
M-107 XC-120 PACK PLANE (M-107B)
M-110 USAF C-119B/C/D/E/F/G; Navy R4Q-1 FLYING BOXCAR and R4Q-2
M-121 high speed biplane intercontinental SAC bomber project (XB-52 competition)
M-122 track gear installation was retrofitted on Boeing B-29 (project)
M-123 track gear installation was retrofitted on Boeing B-50 (project)
M-126? C-119B FLYING BOXCAR
M-128 long range special attack aircraft project with jettisonable auxiliary wing
M-129 USAF T-31 trainer developed from M-91
M-142 engine proposal
M-144 no data
M-159 projected helicopter from American Helicopter Co.
M-160 XC-119H SKYVAN
M-162 no data
M-164 C-119H SKYVAN with 4 x P&W R-2800 (M-164C) (project)
M-167 YC-128/YC-119D & E FLYING BOXCAR with cargo pod (project)
M-172 Global Bomber study (project)
M-175 Projected pulse jet pack helicopter from American Helicopter Co.
M-185 4-engined high wing utility jet transport/business jet projects, engines in 2 underwing pods (M-185A/B/F)
M-186 Jet bomber / twin engined jet transport with a kind of crescent wing (M-186/B/C)
M-189 M-189A no data
M-192 no data
M-194 C-119 FLYING BOXCAR Advanced Base Version (study)
M-195 high altitude reconnaissance plane, competitor project of X-16 and U-2, 1 x P&W J57-P-37 (project)
M-197 STOL aircraft project with 4 x T-55 turboprops
M-203 C-119J FLYING BOXCAR
M-205 C-123B/C/D/H?/J? PROVIDER, YC-123E PANTOBASE
M-206 Modification of C-123 PROVIDER with 2 x Allison T56-A (project)
M-208 Army Unit Support Aircraft project, Pi-Tail aircraft design with 2 x turboprops (M-208B)
M-209 C-119J FLYING BOXCAR (or confusion with M-203?)
M-216 no data
M-219 military transport aircraft project, a C-123 derivative?
M-220 no data
M-222 Whill-ski kit conversion of C-123
M-224 S/VTOL Army VZ-5-FA FLEDGLING research aircraft (M-224-1)
M-225 Swept low-wing executive jet business project, 4 engines in the rear fuselage, 7 seats
M-226 proposed Pi-Tail transport version of C-123B, project only
M-230 XSM-73 BULL GOOSE (WS-123A) decoy missile / also GOOSE production version?
M-231 projected STOL version of C-123B PROVIDER (M-231/B)
M-232 DRAGONFLY twin-boom military STOL project, lateral propellers, 2 x central 800hp Lyc. SO-580 (1956)
M-236 no data
M-252 AN/USD-5 OSPREY (XE-1/XE-2) surveillance drone program (M-252/C)
M-253 TURBOBOXCAR project, based on C-123 PROVIDER with 4 x Lycoming T55 turboprop engines (1957)
M-255 Carrier Onboard Delivery Transport proposal, C-123 mod., aerial resupply of carrier task groups at sea (1957)
M-258 Fairchild F-27 military conversion, planned for procurement as C-138 then cancelled (M-258G/H/J/K)
M-262 no data
M-268 VTOL turboprop transport project (M-268C)
M-270 Logistic transport jet aircraft project 4 x JT3D-4 of 18,000 lbs thrust each (M-270/D)
M-280 AN-USD-5 (XE-2) DRONE BOOSTER multipurpose drone weapon system (M-280) (mock-up made)
M-284 no data
M-286 big jet airliner project
M-288 executive transport aircraft project
M-290 SEA SKIMMER huge logistics wing-in-ground transport aircraft project for transoceanic flight
M-294 FRIENDSHIP. STOL version for the US Navy / standard version for Strategic Air Command
M-398 Heat Shield, 1963
M-450 no data
M-473 YC-123H, (U)C-123K PROVIDER
M-484 YC-119K, C-119K, C-119L, EC-119L FLYING BOXCAR
M-490 Tank
M-491 Tank
M-492 instruments?
M-522 Tank
M-527 Disseminator, tank
M-534 NASA Outsize Booster Carrier Aircraft, utilized a B-36J airframe and engines (Aircraft-Missiles Division)
M-538 FH-227 FRIENDSHIP
M-541 STOL Tactical Airlift Transport with 2 x T64 + 2 x J85 turbojets, would have become the C-123L (-123S?)
M-616 AERCAB aircrew escape rescue capability for combat aircraft
Non-sequential/dubious designations :
M-1942 proposal for modification of C-119C airplane (1949)
M-3028 no data
M-3102 no data
XF-21 possible Model 21 prototype, or erroneous transcription?
PD 19 no data
D-100 Project D-100 (no data)
300 no data
A-400 A-400 AVS variable sweep wing project (with Germany)
Unknown designations :
? SST project (same as Republic SST REP-10 project?)
? SD-3 surveillance drone
? SD-4 surveillance drone
? SD-35 surveillance drone
? J83 jet engine
? AT-21MM GUNNER project, 1943
? C-119K GUNSHIP I
? C-119K GUNSHIP II
? AC-119G GUNSHIP III
? KAQ-1/XSAM-2/CTV LARK missile
? AUM-N-2 PETREL missile
? KUN-1/XASM-N-5 GORGON missile