Editing Northrop F-5 (section)

===Design evolution===
Using a pair of J85s as the baseline, the team began considering a series of prospective designs. Among the earliest concepts was the N-156TX of March 1955. This mounted the engines in pods, one under each wing about mid-span. The fuselage was quite slim compared to the final design, with a crew of two under a narrow cockpit canopy.<ref name=f1960>''Flight'', 8 January 1960, pp. 46-47</ref>

That year, the [[US Navy]] expressed an interest in a fighter to operate from its [[escort carrier]]s, which were too small to operate the Navy's existing jet fighters. Northrop responded with a radical redesign, PD-2706, which placed the engines against the fuselage in short ducts exiting in front of the tail area, like the F-4, and moved the elevator up to form a [[T-tail]]. The resulting design had a much shorter fuselage and was quite compact.<ref name=f1960/> Development along these lines ended when the Navy decided to withdraw the escort carriers. Northrop continued development of the N-156, both as a two-seat advanced trainer, designated as N-156T, and a single-seat fighter, designated as N-156F.<ref>{{harvnb|Paloque|2013|pp=4–7}}.</ref>

[[File:Northrop YF-5A.jpg|thumb|The first Northrop YF-5A prototype]]
Another highly influential figure was chief engineer Welko Gasich,<ref>{{harvnb|Garrison|2005}}.</ref> who convinced Schmued that the engines must be located within the fuselage for maximum performance.<ref name="s7">{{harvnb|Stuart|1978|p=7}}.</ref> This led to the January 1956 PD-2812 version which began to look a lot like the final product, although this version had a long-span low-mounted elevator with notable anhedral. March 1956's PD-2832 moved to a more conventional elevator and had a strongly swept vertical stabilizer. The design underwent several further versions over the next year which experimented with different nose designs and continued to lengthen the fuselage. The final design, PD-2879D, emerged in December 1956.<ref name=f1960/>

Gasich also introduced the concept of "life cycle cost" into fighter design, which provided the foundation for the F-5's low operating cost and long service life. A Northrop design study stated "The application of advanced technology was used to provide maximum force effectiveness at minimum cost.  This became the Northrop philosophy in the development of the T-38 and F-5 lightweight trainer and fighter aircraft."<ref name="s7"/>