70,000 pilots and over 50 years of service have to tell you something. The slide rule packing engineers from Northrop did something right in 1959. After the initial deployment of supersonic aircraft to the front lines of the USAF it became evident that a trainer was needed to develop pilot skills at high speeds. Northrop answered the call with the T-38 Talon, sister to the F-5 Tiger II fighter. While the aircraft was developed without a firm contract it was quickly snapped up by the USAF which ended up operating over 1100 of the sleek jets.
Compared to its contemporaries the T-38 is an elegant, slim design. It's razor sharp wings are only 25 ft from tip to tip. That is 13 ft narrower than the F-4. It was also weighed 23,000 lbs less at 7,200 lbs.
Powered by two 2000 lb thrust GE J85-5A after burning engines, the light weight trainer could reach Mach 1.3. Its speed and maneuverability allows beginning fighter jocks to get a taste of what flying the big jets is like.
The T-38 was quick enough and maneuverable enough that the Thunderbirds picked up the jet in the '70s during the fuel crunch. Really, while the trainer was a bit of a step down from the fire breathing, and smoking, F-4, it was more than a match in the tight turning category. The Talon also looked fairly snazzy in the T-Birds paint.
One of the notable, and public, uses of the T-38 has been as a trainer and transport for NASA astronauts. The plane is used to to keep the astronaut pilot's skills up, allows them to quickly travel around the country and, frankly, to look like astronauts.
Northrop had some very lofty dreams for the T-38. During the early 1960s it was pitched as an "aerospace" trainer for space plane pilots. They had big dreams in the '60s. This version of the T-38 would have had three rocket engines instead of jets and would have been able to reach an altitude of 280,000 ft and a speed of Mach 3.3. That is a heck of a jump from basic trainer. Tony Chong has a great write up of this program. Northrop also looked into making a vertical takeoff version of the aircraft.
The T-38 is still in service. The Air Force is very interested in keeping it in service for some time to come. It has been updated a number of times, has a rigorous structural program and is probably out flying right now training a new pilot.
NASA.gov, Fly-fighter-jet.com, Myhobbielinks.com, Warbirdalley.com, Lloyder.com, Wikipedia.org