In 1952 Northrop began work on a fighter project, the Fang, with shoulder-mounted delta wing and a single engine. The proposed General Electric J79 engine, weighing nearly two tons, meant the resulting aircraft would be large and expensive. Then in 1953, representatives from General Electric Aviation's newly created Small Aircraft Engine Department showed Northrop a relatively tiny engine (around 400 lb installed wt) capable of 2,500 lb of thrust, and Northrop VP-Engineering Edgar Schmued saw the possibility of reversing the trend toward the large fighters. Schmued and chief engineer Welko Gasich decided on a small twin-engine "hot-rod" fighter, the N-156. Northrop began its N-156 project in 1954, aiming for a small supersonic fighter jet capable of operating from the US Navy's escort carriers. However, when the Navy chose not to pursue equipping its fleets in that fashion, Northrop continued the N-156 design using in-house funding, recasting it as a lightweight fighter (dubbed N-156F) and aimed at the export market.
In the mid-1950s the USAF issued a General Operating Requirement for a supersonic trainer, planning to retire its 1940s-era Lockheed T-33s. Northrop officials decided to adapt the N-156 to this competition. The only other candidate was the two-seat version of the North American F-100 Super Sabre. Although the F-100 was not considered the ideal candidate for a training aircraft (it is not capable of recovering from a spin), NAA was still considered the favorite in the competition due to that company's favored-contractor status with the Air Force. However, Northrop officials convincingly presented life-cycle cost comparisons which could not be ignored, and they were awarded the contract, receiving an order for three prototypes. The first (designated YT-38) flew on 10 March 1959. The type was quickly adopted and the first production examples were delivered in 1961, officially entering service on 17 March that year, complementing the T-37 primary jet trainer. When production ended in 1972, 1,187 T-38s had been built (plus two N-156T prototypes). Since its introduction, it is estimated that some 50,000 military pilots have trained on this aircraft. The USAF remains one of the few armed flying forces using dedicated supersonic final trainers, as most, such as the US Navy, use high subsonic trainers.
The T-38 is of conventional configuration, with a small, low, long-chord wing, a single vertical stabilizer, and tricycle undercarriage. The aircraft seats a student pilot and instructor in tandem, and has intakes for its two turbojet engines at the wing roots. Its nimble performance has earned it the nickname white rocket. In 1962 the T-38 set absolute time-to-climb records for 3,000, 6,000, 9,000 and 12,000 meters, beating the records for those altitudes set by the F-104 in December 1958. (The F-4 beat the T-38's records less than a month later.)
The F-5B and F (which also derive from the N-156) can be distinguished from the T-38 by the wings; the wing of the T-38 meets the fuselage straight and ends square, while the F-5 has leading edge extensions near the wing roots and wingtip launch rails for air-to-air missiles. The wings of both the T-38 and the F-5 family use conventional skin over spar-rib structure.
Most T-38s built were of the T-38A variant, but the USAF also had a small number of aircraft converted for weapons training (designated AT-38B), which were fitted with a gunsight and could carry a gunpod, rockets, or bombs on a centerline pylon. In 2015, 504 T-38s were still operational with the USAF, with many more in operation around the world. Most of the USAF variant aircraft (T-38A and AT-38B) have been converted to the T-38C through an avionics upgrade program. Improvements include the addition of a HUD, GPS, INS (Inertial Navigation System), and TCAS. Most jets have also received PMP (a propulsion modification to improve low-altitude engine thrust). Approximately a third of the fleet (those that experience more severe usage) are currently undergoing structural replacements and upgrades, as well as receiving new wings, to extend their service life to 2029.
The fighter version of the N-156 was eventually selected for the US Military Assistance Program and produced as the F-5 Freedom Fighter. Many of these have since reverted to a weapons training role as various air forces have introduced newer types into service. The F-5G was an advanced single-engined variant later renamed the F-20 Tigershark.
- N-156T: Northrop company designation.
- YT-38: Prototypes, two built with YJ85-GE-1 engines, later designated YT-38A and four pre-production aircraft with YJ-85-GE-5 engines, later designated T-38A.
- T-38A: Two-seat advanced training aircraft, production model, 1,139 built.
- T-38A(N): Two-seat astronaut training version for NASA. See T-38N below.
- AT-38A: A small number of T-38As were converted into weapons training aircraft.
- DT-38A: A number of US Navy T-38As were converted into drone directors.
- GT-38A: Permanently grounded aircraft, often due to flight or ground mishap, converted into ground procedural trainers or aircraft maintenance trainers.
- NT-38A: A small number of T-38As were converted into research and test aircraft.
- QT-38A: Unmanned target drone aircraft.
- AT-38B: Two-seat weapons training aircraft.
- T-38C: A T-38A with structural and avionics upgrades.
- T-38M: Modernized Turkish Air Force T-38As with full glass cockpit and avionics, upgraded by Turkish Aerospace Industries under the project codename "ARI" (Turkish: Ari, for Bee).
- T-38N: Former USAF T-38As bailed to NASA and T-38As directly assigned to NASA that received an Avionics Upgrade Program (AUP), modernizing communications and navigation systems, replacing outdated avionics, and adding a weather radar, flight management system, altitude alert systems, and modern controls and displays.
- N-205: "Space trainer" variant proposed in May 1958, with triple rocket engines for vertical launch. Capable of Mach 3.2 on its way to an altitude of 200,000 feet (61,000 m).
- ST-38 or N-205B: Revised proposal in April 1963 for the new Aerospace Research Pilot School, with a rolling takeoff, top speed of Mach 3.3 and a ceiling of 285,000 feet (87,000 m), high enough to qualify its pilots for astronaut wings.
- T-38 VTOL Proposed vertical takeoff variant with four lift nozzles behind the pilot.