After Lockheed had introduced its 10-passenger Model 10 Electra, the company decided to develop a smaller version which would be better suited as a "feeder airliner" or a corporate executive transport.
At the same time, the U.S. Bureau of Air Commerce had also sensed the need for a small feeder airliner and announced a design competition for one.
In order for a candidate to qualify for the competition, a prototype had to fly by June 30, 1936.

Lockheed based its candidate, which it named the Model 12 Electra Junior, around a scaled down Electra.
It would carry only six passengers and two pilots but would use the same 450 hp (340 kW) Pratt & Whitney R-985 Wasp Junior SB radial engines as the main Electra version, the 10A. This made it faster than the Electra, with a top speed of 225 mph (362 km/h) at 5,000 ft (1,500 m).
Like the Electra, the Model 12 had an all-metal structure, trailing-edge wing flaps, low-drag NACA engine cowlings, and two-bladed controllable-pitch propellers (later changed to constant-speed propellers).
It also had the Electra's twin tail fins and rudders, which were becoming a Lockheed trademark.
The landing gear was a conventional tail-dragger arrangement, with the main wheels retracting backwards into the engine nacelles; as was often the case with retractable gear of the period, the wheel bottoms were left exposed in case a wheels-up emergency landing was necessary, or the pilot simply forgot to deploy his novel landing gear.

As in the Electra and the Boeing 247, the Model 12's main wing spar passed through the passenger cabin; small steps were placed on either side of the spar to ease passenger movement.
The cabin had a lavatory in the rear.
Although the standard cabin layout was for six passengers, Lockheed also offered roomier, more luxurious layouts for corporate or private owners.

The new transport had its first flight on June 27, 1936, three days before the competition deadline, at 12:12 PM local time, a time deliberately chosen for the Model 12's number.
As it turned out, the other two competition entries, the Beechcraft Model 18 and the Barkley-Grow T8P-1, weren't ready in time for the deadline, so Lockheed won by default.
The "Electra Junior" name did not catch on in the way that the original Electra's name had.
Most users simply referred to the aircraft by its model number, as the Lockheed 12.

The original Lockheed 12 version, with Wasp Junior engines, was the Model 12A. Almost every Lockheed 12 built was a 12A or derived from the 12A. There was also a Model 12B, using 440 hp (330 kW) Wright R-975-E3 Whirlwind radials, but only two of this model were built.
Although Lockheed had also announced a Model 12F, powered by Wright R-760 Whirlwind seven-cylinder radials, and a Model 12M, powered by 290 hp (220 kW) Menasco six-cylinder inline engines, neither of these versions reached production.
After Lockheed had introduced its 10-passenger Model 10 Electra, the company decided to develop a smaller version which would be better suited as a "feeder airliner" or a corporate executive transport. At the same time, the U.S. Bureau of Air Commerce had also sensed the need for a small feeder airliner and announced a design competition for one. In order for a candidate to qualify for the competition, a prototype had to fly by June 30, 1936.
Lockheed based its candidate, which it named the Model 12 Electra Junior, around a scaled down Electra. It would carry only six passengers and two pilots but would use the same 450 hp (340 kW) Pratt & Whitney R-985 Wasp Junior SB radial engines as the main Electra version, the 10A. This made it faster than the Electra, with a top speed of 225 mph (362 km/h) at 5,000 ft (1,500 m). Like the Electra, the Model 12 had an all-metal structure, trailing-edge wing flaps, low-drag NACA engine cowlings, and two-bladed controllable-pitch propellers (later changed to constant-speed propellers). It also had the Electra's twin tail fins and rudders, which were becoming a Lockheed trademark. The landing gear was a conventional tail-dragger arrangement, with the main wheels retracting backwards into the engine nacelles; as was often the case with retractable gear of the period, the wheel bottoms were left exposed in case a wheels-up emergency landing was necessary, or the pilot simply forgot to deploy his novel landing gear.
As in the Electra and the Boeing 247, the Model 12's main wing spar passed through the passenger cabin; small steps were placed on either side of the spar to ease passenger movement. The cabin had a lavatory in the rear. Although the standard cabin layout was for six passengers, Lockheed also offered roomier, more luxurious layouts for corporate or private owners.
The new transport had its first flight on June 27, 1936, three days before the competition deadline, at 12:12 PM local time, a time deliberately chosen for the Model 12's number. As it turned out, the other two competition entries, the Beechcraft Model 18 and the Barkley-Grow T8P-1, weren't ready in time for the deadline, so Lockheed won by default. The "Electra Junior" name did not catch on in the way that the original Electra's name had. Most users simply referred to the aircraft by its model number, as the Lockheed 12.
The original Lockheed 12 version, with Wasp Junior engines, was the Model 12A. Almost every Lockheed 12 built was a 12A or derived from the 12A. There was also a Model 12B, using 440 hp (330 kW) Wright R-975-E3 Whirlwind radials, but only two of this model were built. Although Lockheed had also announced a Model 12F, powered by Wright R-760 Whirlwind seven-cylinder radials, and a Model 12M, powered by 290 hp (220 kW) Menasco six-cylinder inline engines, neither of these versions reached production.
Lockheed Model 12 Electra Junior