u/bob_the_impala

In the 1950s, Northrop developed two new light aircraft, the N-156F fighter and the N-156T trainer. The USAF assigned the designations F-5A to the single-seat fighter version and T-38A to the two-seat trainer version. Eventually, a two-seat trainer version of the F-5A was developed as the F-5B. Later, an improved fighter was developed as the F-5E, with a corresponding two-seat trainer version, the F-5F.

The T-38 was mainly used by the USA, with exports to a few other countries. The F-5 was built in larger numbers, including license production in other countries, and was widely exported. Some of the main differences between the T-38 and the F-5 include the following:

• The T-38 has a simple wing with trailing-edge flaps and ailerons, but no leading-edge flaps.
• The F-5 has a more advanced wing with leading-edge flaps and wing root leading-edge extensions.
• While the F-5 has wingtip fuel tanks or missile rails, the T-38 does not.
• The F-5 has four underwing hardpoints for various external stores. The T-38 has no underwing hardpoints.
• Both the F-5 and T-38 have one centerline hardpoint. For the T-38, it does not seem to be used very often, typically only for a baggage pod. The AT-38B weapons training version could mount a gun pod, rockets, or bombs on the centerline hardpoint.
• The T-38 has relatively small, simple air intakes with a slanted forward edge.
• NASA later designed an improved, enlarged intake for the T-38 with a straight forward edge, which has been installed on many existing T-38 trainers.
• The F-5 has enlarged air intakes, with a horizontal upper edge which curves down to a vertical rear edge.
• The nose and forward fuselage of the T-38 and F-5B are similar, but the F-5F has a lengthened forward fuselage with a flatter, tapered nose.
• The F-5A and F-5E have two guns in the upper nose. The F-5B and T-38 do not have internal guns. The F-5F has only one gun in the nose.

There are a few other subtle differences, but those are the most obvious.

If the air intakes are clearly visible, then this is the easiest way to distinguish between a T-38 and F-5B/F. Here is a USAF T-38 with the original slanted intakes:

Source: https://www.dvidshub.net/image/9148211/beale-afb-t-38s-fly-above-california-air-space

Here is a USAF T-38 with the new, enlarged intakes. Note also the clean wing with no wingtip mounts or underwing hardpoints for external stores.

Source: https://www.dvidshub.net/image/9477629/student-pilots-hone-skills-t-38-training-sortie

Here is an F-5B. In addition to the different air intake, note also the the wingtip fuel tanks and underwing hardpoints.

Source: https://commons.wikimedia.org/wiki/File:F-5_(5081072465).jpg

Here is an F-5F. Note the lengthened nose, different intakes (compared to the T-38), as well as the wingtip missile rail, underwing hardpoint, and leading-edge flap.

Source: https://commons.wikimedia.org/wiki/File:J-3210_Vista.JPG

From F-5 in action, squadron/signal publications

From Wikipedia and F-5 in action, squadron/signal publications

References:

• Wikipedia Northrop T-38 Talon
• Wikipedia Northrop F-5
• Tech Briefs Improved Inlets for T-38 Airplane
• Joe Baugher Northrop F-5 Freedom Fighter/Tiger II