"COinter-INsurgency" ("COIN") aircraft are a specialized breed of warplane designed to attack and contain insurgent/guerilla forces. This generally defines an airframe capable of long loitering times with inherently excellent low-altitude, low-speed controlling. During the 1950s and 1960s, there proved a need for such aircraft for the various low-level conflicts emerging across the globe after World War 2 (1939-1945). During this period, the Fletcher FD-25 "Defender" was developed by one John Willard Thorp (1912-1992), an aerospace engineer with extensive experience in light and very-light aircraft.
While it failed to impress the United States military, it went on to see limited sales to foreign parties in Cambodia (6) and Vietnam (4) by way of Japan-based Toyo - the company having purchased the rights to the American aircraft. Cambodia took on three single-seat attackers along with three twin-seat trainer variants.
The FD-25 development phase constituted three total prototype forms of which a pair was built to the basic single-seat standard. The third offering became a twin-seat derivative. The aircraft flew for the first time in 1953 and, true to form, was a lightweight, single-seat, single-engine platform with low-mounted straight mainplanes and a conventional tri-plane tail unit (single rudder). The undercarriage remained fixed during flight and was of the "tail-dragger" configuration. At center mass of the aircraft was the single-seat cockpit under a clear view canopy offering excellent vision. Construction of the warplane was largely of metal.
Dimensions of the light aircraft included a running length of 20.10 feet, a wingspan measuring 30 feet, and a height of 6.2 feet. Empty weight reached 1,230lb against an gross weight near 2,500lb.
Each wing mainplane was given four weapons hardpoints to which various air-launched and air-dropped munitions could be affixed, as well as fuel tanks to increase operational ranges. Typical supported stores included 2 x 250lb conventional drop bombs and air-launched rockets of various caliber - 4 x 127mm, 20 x 80mm, or 40 x 70mm. The mainplanes were also home to 2 x 7.62mm machine guns embedded in each member, these in fixed, forward-firing mountings.
Performance was handled by a single Continental E-225-8 series 6-cylinder air-cooled piston engine developing 225 horsepower and driving a two-bladed propeller unit at the nose. Specifications included a maximum speed of 190 miles-per-hour, a cruising speed near 160mph, a range out to 630 miles, and a service ceiling up to 16,500 feet. Rate-of-climb reached 1,725 feet-per-minute.
Including the aforementioned prototypes, just thirteen FD-25 Defender aircraft were completed in all.