Authored By Dan Alex (Updated: 5/11/2016):
Compared to the T-37, the A-37 was given several notable modifications for the light attack role. Its undercarriage and wings were reinforced and wingtip fuel tanks were increased in size to promote better loitering times and operational ranges. The fuselage also accepted an internal General Electric Minigun Gatling system for close-range strafing. The cockpit was updated to include modern USAF weapons support, navigation and communications equipment. Each wing was initially granted use of three hardpoints and cleared to carry various types of USAF ordnance in inventory. The crew of two remained from the original Tweet and were seated in a side-by-side arrangement complete with the original's dual control scheme. Vision was largely good thanks to the lightly-framed canopy. The aircraft was powered by 2 x General Electric J85-J2/5 turbojet engines with approximately 2,400lbs of thrust output each.
From this revision was born the "YAT-37D" prototype used to prove the platform viable to USAF authorities. First flight was recorded in October of 1964 and, after a period of growing disinterest in the type which delayed service entry, mounting losses of other close-support systems forced USAF attention back onto the A-37 project. A second prototype was added during testing and this model included an additionally pair of weapons pylons for greater munitions support. The YAT-37D then graduated from its testing role into the "AT-37D" which then evolved to the finalized "A-37A" designation and subsequent production models.
As completed, the A-37 was given a wide, squat forward fuselage which tapered rather nicely to the rear. The wings were straight in their design and capped by wingtip fuel tanks. Underwing pylons were held well outboard of the fuselage. The twin engine arrangement, buried in the fuselage, was aspirated by a pair of small intakes to either side of the aircraft. The empennage included a single vertical tail fin with mid-set horizontal planes. The undercarriage was wholly retractable and short, leading to the aircraft having a very low profile when at rest.