This was brought up by queries as to why the leap from B-2 to B-21 skipping over a bunch of numbers.
Number systems have been played with through the years, usually to try to fool the public/congress that something is not a new project.
Examples:
XP-52 and XP-59 were Bell pusher, twin boom, swept wing (long before Me262!) fighter programs intended for stillborn Continental V12 XIV-1430 and R-2800. First USAAF jet P-59A was given designation for secrecy and disinformation.
FJ Fury was straight wing, FJ-2 entirely new swept wing based on F-86, FJ-4 was total redesign w/new engine.
F-86D bore no relation to other Sabres with completely different mission. Later versions were designated F-95 when a new designation fit better in new procurement procedures
U-2 was purposely given designation of light liaison aircraft to help escape notice
P-75 was designated out of order as the publicists of the heavily promoted super fighter thought it was a more catchy number. Some source claim Preston Tucker was involved with promoting this.
F9F-5 straight wing Panther morphed into swept wing F9F-6 Cougar as a contract extension, not requiring new approval
F4H/F-4 Phantom started as AH-1, single seat attack bomber, and evolved into two seat multi role fighter
F-84 went through pretty much same process to emerge as entirely new bent wing F-84F
XF-106 was originally based on F-84F bits with XT-40 turboprop squeezed in (Thunderscreech) but then back-designated to become XF-84H. Convair picked up the designation for their Delta Dart
F-86C was developed for long range escort role, and went through many changes to emerge as YF-93
F-98 Falcon and F-99 Bomarc were guided missiles given fighter designations to ease contracting. Also B-61 Matador/Mace and B-62 Snark IRBM/ICBM missiles.
B-36G mounted a swept back wing with 8 jet engines on the piston engine bomber, also sweeping the empennage. Wound up being designated YB-60
many more can be listed such as Grumman Super Tiger, and Vought Super Crusader and XF-88B Voodoo w/turboprop
Number systems have been played with through the years, usually to try to fool the public/congress that something is not a new project.
Examples:
XP-52 and XP-59 were Bell pusher, twin boom, swept wing (long before Me262!) fighter programs intended for stillborn Continental V12 XIV-1430 and R-2800. First USAAF jet P-59A was given designation for secrecy and disinformation.
FJ Fury was straight wing, FJ-2 entirely new swept wing based on F-86, FJ-4 was total redesign w/new engine.
F-86D bore no relation to other Sabres with completely different mission. Later versions were designated F-95 when a new designation fit better in new procurement procedures
U-2 was purposely given designation of light liaison aircraft to help escape notice
P-75 was designated out of order as the publicists of the heavily promoted super fighter thought it was a more catchy number. Some source claim Preston Tucker was involved with promoting this.
F9F-5 straight wing Panther morphed into swept wing F9F-6 Cougar as a contract extension, not requiring new approval
F4H/F-4 Phantom started as AH-1, single seat attack bomber, and evolved into two seat multi role fighter
F-84 went through pretty much same process to emerge as entirely new bent wing F-84F
XF-106 was originally based on F-84F bits with XT-40 turboprop squeezed in (Thunderscreech) but then back-designated to become XF-84H. Convair picked up the designation for their Delta Dart
F-86C was developed for long range escort role, and went through many changes to emerge as YF-93
F-98 Falcon and F-99 Bomarc were guided missiles given fighter designations to ease contracting. Also B-61 Matador/Mace and B-62 Snark IRBM/ICBM missiles.
B-36G mounted a swept back wing with 8 jet engines on the piston engine bomber, also sweeping the empennage. Wound up being designated YB-60
many more can be listed such as Grumman Super Tiger, and Vought Super Crusader and XF-88B Voodoo w/turboprop