Not in the US. P-38 Lighting P-39 Airacobra P-40 Warhawk P-47 Thunderbolt P-51 Mustang P-80 Shooting Star F-35 Lightning II F-84 Thunderjet F-86 Saberjet Why the gaps? In the early days, it was due to airplane manufacturers running designs simultaneously to sell to the War Department. When a plane was accepted, the numerical designation used by the designer was generally kept.

There's an excellent article online covering this topic: http://home.att.net/~jbaugher1/Fdesig.html In a nutshell, the Army Air Forces and Navy used divergent numbering schemes for decades. After a previously confusing numbering scheme, the USAAF designated pursuit aircraft in the order in which they were commissioned. The P-38 Lightning, then, was the 38th pursuit aircraft design commissioned by the USAAF. This numbering scheme continued for the USAAF almost without interruption from P-1 through 1948 (the lone exception being P-74), when the Air Force was born as a separate service. With the advent of the Air Force, pursuit aircraft were redesignated fighter aircraft, but the numbering continued apace, skipping F-109 for some reason, up to the F-111, where it stopped. The Navy, meanwhile, had a numbering system that identified each aircraft primarily by manufacturer, which it had the good sense to abandon after it had been ordered to do so in 1962. The Navy aircraft then in service were redesignated according to the new scheme ("F" for fighters), beginning with F-1. This united the Navy's and Air Force's numbering schemes, and each new fighter aircraft for either the Navy or the Air Force now draws from this pool. The first dedicated Air Force plane on the new list is the F-5 Freedom Fighter, though it was primarily an export plane. The Blackbird's YF-12 fighter variant didn't go very far, either, leaving the F-15 Eagle as the first frontline Air Force Fighter with the new designation. 13 was skipped for superstition, and 19 was ostensibly skipped (no publicly acknowledged aircraft carries this designation), though it appears the F-117 was deliberately misnumbered to confuse the outside world. The YF-17 became the F-18 after much modification; the F-20 was a short-lived export program, a variant of the F-5E, which itself was a variant of the T-38; the F-21 is an aggressor-only aircraft (a small number of Israeli fighters for training); and the YF-23 lost to the F-22 Raptor. The numbers between 24 and 33 are (at least partly) used for experimental aircraft, both by the Air Force and by NASA, such as the X-29 forward-swept wing and the X-30. The YF-34 lost to the F-35.