Ground Attack Experimental
Two single-engine attack biplanes designed by Army engineers around an experimental 700-hp Engineering Division W-lA-18 engine were ordered December 20, 1920, from Boeing. Like the GA-l, this three-place GA-2 sacrificed performance for ferocity and was first flown December 18, 1921.
Mounted behind the engine, at the leading edge of the lower wing, was a 37-mm cannon and two .30-caliber guns movable 60° in the vertical plane and 15° in the horizontal. The gunner sat beneath the pilot and also had a .50-caliber Browning to fire back and down, while the third crewman in a turret behind the pilot guarded the upper hemisphere with two Lewis guns. Ten 20-pound bombs could be attached to wing racks. Protection from ground fire was furnished by 1,600 pounds of 1/4-inch armor and the duplication of all struts, bracing and control wires, and spars. The GA-2 is the sole example of this weighty and expensive safety device.
The general failure of these armored ground-strafers was due to inadequacies of the time’s engineering: not enough strength and power, and too much weight and drag. All through the decade following the war, therefore, attack-squadron equipment, like that of the observation outfits, had to be drawn from the wartime stock of DH-4s.
The most advanced aircraft style of that time was the all-metal, Junkers monoplane whose low wing was thick enough to allow a cantilever structure without outside supporting struts. A New York dealer, John Larsen, imported from Germany several Junkers F13 cabin planes built of corrugated dural.
Two designated JL-6 with a 243-hp 6-cylinder BMW engine were purchased by the Army in 1920. Larsen also modified another as the JL-12 attack by installing a 420-hp Liberty 12 engine, replacing the German metal skin with .025-inch Alcoa duralumin, twice the original thickness, and 400 pounds of 1/8-inch armor.
Thirty Thompson M1921 submachine guns with 3,000 rounds of .45-caliber ammunition were added. Two “Tommy guns” could be fired out of the cabin windows on each side, while the rest were fixed to fire downward. The 28 belly guns were mounted in the floor; twelve pointed slightly forward, six directly down, and ten inclined to the rear. Half the guns could be fired at once, or a single trigger could set off all 28, delivering a fire volume for once justifying the cliché about a rain of bullets. While the JL-12 was offered to the Army in December 1921, the test pilot opposed purchase of the plane, described as a bad flier, expensive, and with an pistol-caliber armament array of doubtful efficiency.
The last prototype actually ordered by the Army in 1920 was a light bomber of advanced layout. Stimulated by the success of the Junkers metal internally-braced low-wing monoplanes, the two Gallaudet DB-l monoplanes contracted on December 24, 1920, were low-wing two-seaters without any struts outside of the thick wing. Powered by a 700-hp Engineering Division W-lA 18-cylinder water-cooled engine, the all-metal DB-l (Day Bomber One) design promised to carry 600 pounds of bombs with eight hours of fuel and have a top speed of 141 mph.
But when the first DB-l was delivered on December 5, 1921, it proved to be overweight; 9,207 pounds empty instead of the 7,050 pounds estimated. When the control system made the duralumin skin buckle, it was decided unsafe to fly the monoplane, but to use it only for static tests.
On March 11, 1922, the second example was reordered as the DB-lB with a lighter structure of welded steel tubing with fabric covering on the rear fuselage, wing sections, and control surfaces. Between the pilot and gunner’s cockpit was a bay for the 600-pound bomb load and 1,367 rounds were carried for four .30-caliber guns; a Browning in the nose, two Lewis guns in the rear cockpit, and one in the belly.
Careful testing of structural components delayed delivery to McCook Field until May 26, 1923, and the first flight until August 1. New difficulties delayed any more flights until April 1924, and the design seemed too advanced for the structural technique of that time. Gallaudet General Manager Rueben Fleet advised against any more flight tests.