The first G.12 trimotor transport was flown in October, 1940. Designated G.12C (Civile), the fourteen-passenger airliner was designed for high-altitude trans-Alpine routes. The power units were FIAT A.74 R.C.42 fourteen-cylinder radials of 170 h.p. each. Structure was of metal with mixed metal and fabric covering. Empty and loaded weights were 20,680 lb., and 34,100 lb. Maximum speed was 242 m.p.h. at 16,400 ft., cruising speed 192 m.p.h., ceiling 27,880 ft., and range 1962 miles. One civil airliner was placed in service with Avio Linee Italiane S.A. on the Milan-Venice-Vienna-Budapest route, but further wartime development was concentrated on military models.
The G.12T cargo and troop transport, which could carry 22 fully-equipped troops, flew in May, 1941; this version was placed in production for the Regia Aeronautica and saw service in North Africa as well as in metropolitan Italy. The G.12T weighed 20,460 lb. empty and 33,000 lb. loaded and had a range of 1428 miles, other performance figures being similar to those of the G.12C. Dimensions common to most models of the G.12 were: span 93 ft. 10 in., height 65 ft. 1P/3 in., height 16 ft. 1 in., and wing area 1215.9 sq. ft.
The G.12 Gondar (named after the base in A.O.I. which was one of the objectives during the Ethiopian war of 1935) was a further model of which several examples were built in 1941. Empty and loaded weights were 20,570 lb. and 37,059 lb., and range was no less than 3606 miles, a distance greater than that from the FIAT factory in Turin to Gondar. Maximum speed dropped slightly to 239 m.p.h. In 1942 one G.12A (Grande Autonomia, or long range) passenger airliner was built. In keeping with its designation, the G.12GA had an impressive range of 4350 miles. Maximum speed was 236 m.p.h. and ceiling 21,320 ft. Empty and loaded weights were 21,340 lb. and 39,600 lb.
Later the same year appeared the first G.12LGA passenger transport, of which a few were built for LATI (Linee Aeree Transcontinentale Italiane), the airline founded in September, 1938, to link Italy with South America. The G.12LGA was powered by 750 h.p. Alfa Romeo 126 R.C.34 nine-cylinder radials. Empty and loaded weights were 20,460 lb. and 34,100 lb. Performance included a maximum speed of 233 m.p.h., a ceiling of 19,680 ft., and a range of 2142 miles.
In late 1942 and early 1943 came the G.12RT and G.12RTbis prototypes, both extremely long-range transports powered by 895 h.p. Alia Romeo 128 R.C.18 nine-cylinder radial engines. These two aircraft, although operating at lower altitudes at reduced speeds, were by far the heaviest and longest-ranged of the entire G.12 series. The G.12RT, weighing 21,197 lb. empty and 43,802 lb. loaded, had a ceiling of 15,580 ft. and a range of 4968 miles. The G.12RTbis carried an even greater fuel load, empty and loaded weights being 22,143 lb. and 46,640 lb., and had a ceiling of 14,100 ft. and a range of 5590 miles, exceeding that of all other wartime Italian aircraft and not greatly inferior to that of the Boeing XPBB-1 flying boat, which at that time was considered to have an exceptional endurance of seventy-two hours and a maximum range of 6300 miles.
Post-war versions of the G.12 built between 1945-50 included the G.12CA nineteen-passenger airliner (Alia Romeo 128 R.C.18 radials), the G.12L 18-22-passenger airliner (FIAT A.74 R.C.42 radials) with lengthened fuselage and modified fin, the G.12LB 16-22-passenger airliner (730 h.p. Bristol Pegasus 48 radials), the G.12LP 18-22-passenger airliner (1065 h.p. Pratt & Whitney R.1830 SlC3G radials), the G.12LA 16-22-passenger airliner (Alia Romeo 128 R.C.18 radials) - all civil models - and the G.12 Aula Volante (Flying Classroom) military trainer (Alia Romeo 128 R.C.18 radials). Commencing with the G.12L in 1947, the later models were of all-metal construction.
The G.212 was a larger, generally similar post-war development built in several versions, with accommodations for as many as 34 passengers. Wing span and area were increased to 96 ft. 3 in. and 1254.6 sq. ft. respectively. Performance was similar to the various models of the G.12.