When the trainer was first developed in 1942, it utilized two Ampro 16mm sound projectors, a 12 ft x 12 ft (3.66m x 3.66m) screen, and a mock .50-caliber (0.5 in/12.7mm) machine gun – the projector system was placed 12 ft (3.66m) from the screen. The student sat between the projectors and the screen and would shoot "light bursts” with the mock gun at enemy aircraft that were projected onto the screen by one of the 16mm projectors.  

The enemy aircraft 16mm film opened with a title card: “Aerial Gunnery Training Film – Prepared for the US Army Air Force, U.S. Navy Air Force – by the Jam Handy Organization”. This was followed by a title card indicating the type of aircraft the trainee was supposedly flying in, as well as the speed that they are traveling at. The films then featured brief sequences of single enemy planes attacking them. The sequences were composed of realistic model airplanes of enemy aircraft, flying against a painted backdrop. These planes were moved in a way that accurately simulated the movement of the particular aircraft. Each sequence identified the type of enemy aircraft attacking them and provided information on the wingspan and length of fuselage. Throughout the film, the constant sound of airplane engine noise was heard. Before the opening title card, the film featured a special leader to synchronize the film with a second “polarized light” film. The maximum length of the films was 1,600 ft (487.68m).

As the enemy aircraft film ran, a second 16mm film was synchronized to it, which projected a circle (or target shape) onto the screen using polarized light. This polarized target instructed the student where, and when, to shoot. The trainee would aim and shoot his mock gun at the screen – as the trainee pulled the trigger, the gun projected "light bursts” onto the screen, revealing the student’s aim and timing to the instructor. Polarizing the light to the “target film” allowed two training modes: one, where both instructor and trainee could see both primary and secondary films superimposed; and, a second, where the trainee would wear a pair of polarized glasses, preventing them from seeing the polarized “target”. In the latter mode, the instructor was able to see how accurately the student aimed, without the assistance of a visible training target. 

As the war progressed, modifications were made to the Jam Handy Trainer. A mock gun turret was developed, which could mimic the motions of a Boeing B-29 Superfortress bomber turret and was operated by foot pedals. One of the more interesting later iterations was a mechanical scoring device, using infrared technology, referred to as the “3A-20”. A 2-in (50.8mm) spot of infrared light was projected onto the screen, in the same position as the polarized “target” – the mock machine guns contained a photoelectric cell, sensitive in the infrared region of the spectrum, which could detect infrared light reflected back from the screen. If, when the trainee shot his gun at the screen, the photoelectric cell detected reflected infrared light emanating from the projected infrared “target”, the 3A-20 device was able to detect and register when the trainee had hit their targets. It also allowed the Jam Handy Trainer to use “gongs” – machine-gun sounds, and other sound effects, to signal “hits” and “misfires”. The infrared technology also allowed multiple students to use the Jam Handy Trainer at once. While ingenious, the technology had its flaws, and the device was apparently redeveloped and modified on several occasions. Seemingly, three different variations of the 3A-20 were designed during the war – the 3A-20A, 3A-20B and 3A-20C. The model referred to as the 3A-20C is cited as being the most reliable of the three. Due to its flaws, many instructors chose not to use the automatic scoring devices, sticking with the original ‘light burst’ manual-scoring method.