Up until 1920, there was no unified designation scheme for American combat aircraft. Before that time, aircraft had always served under their original manufacturer's designation (e. g. SPAD XIII, DH-4, S.E.5, etc). In 1920, it was decided that some sort of unified designation scheme was needed for American combat planes. In that year, the Army Air Service adopted an official letter-and-number designation scheme for all newly-procured aircraft. The letter would indicate the basic type, and the model number would indicate the sequence number of the particular aircraft in order of procurement within that basic type categeory.
Henceforth, all Army aircraft were to be subdivided into 15 basic categories,
three of which were bomber-type categories:
In the Day Bombardment (DB) category, there was only one entry:
Gallaudet DB-1 Low wing bomber. Only one built.
Here are the Night Bombardment, Short Distance (NBS) entries:
Martin NBS-1 Biplane bomber powered by two Liberty Liquid-cooled engines. LWF NBS-2 Proposal for biplane bomber powered by two Liberty liquid-cooled engines. Not built. Elias NBS-3 Biplane bomber powered by two Liberty liquid-cooled engines. Only one built. Curtiss NBS-4 Biplane bomber powered by two Liberty liquid-cooled engines. Only 2 built.
Here are the entries in the Night Bombardment, Long Distance (NBL) category:
Witteman-Lewis NBL-1 Large triplane bomber powered by 6 engines. Only one built. Martin NBL-2 Proposal for biplane bomber powered by two 700hp W-2779 engines. Not built.
In May of 1924, the system was revised and additional letters were added. Aircraft
already in service retained their original designations, but all new production was
done under the new system. Bombers were now classified according to their size rather
than their role:
Here are the bombers in the LB category:
Huff-Daland LB-1 Biplane bomber powered by one Packard 2A-2540 liquid-cooled engine. 10 built. Fokker-Atlantic LB-2 Monoplane bomber powered by two Packard 2A-2540 liquid-cooled engines. Not built Huff-Daland XLB-3 Biplane bomber powered by two R-1340 radial engines. One built. Martin LB-4 Proposal for all-metal biplane bomber powered by two R-1690 radials. Not built Huff-Daland LB-5 Biplane bomber powered by two Liberty V-1650 engines. 36 built. Keystone LB-6 Biplane bomber powered by two Wright Cyclone radials. 18 built Keystone LB-7 Biplane bomber powered by two Pratt & Whitney Hornet radials. 18 built. Keystone LB-8 Version of LB-7 with geared Pratt & Whitney R-8360-3 radials. One built. Keystone LB-9 Version of LB-7 with geared Wright R-1750 Cyclone radials. One built. Keystone LB-10 Version of LB-6 with single rudder and Pratt & Whitney R-1690-3 radials. Designation changed to B-3 in 1926. Keystone LB-11 Version of LB-6 powered by 2 Wright R-1750-3 Cyclone radials. Only one built. Keystone LB-12 Version of LB-7 with Pratt & Whitney R-1860-1 radials. Only one built. Keystone LB-13 Biplane bomber powered by two Pratt & Whitney GR-1690 radials. Completed as B-4 and B-6 Keystone LB-14 Biplane bomber powered by two Pratt & Whitney GR-1860 radials. Delivered as B-5.
Here are the bombers in the HB category:
Huff-Daland HB-1 Larger and heavier version of LB-1 with one Packard 2A-2540 engine. Only one built. Atlantic HB-2 Projected monoplane bomber with two Packard 2A-2540. Not built Huff-Daland HB-3 Projected monoplane bomber with two Packard 2A-2540. Not built.
Here are the bombers in the B (medium bomber) category:
Huff-Daland XB-1 Twin-engine version of XHB-1. Only one built Curtiss B-2 Condor Twin-engined biplane bomber. Two Curtiss V-1570 liquid-cooled engines. 12 built.
One of the categories that had been introduced in 1924 was B, which originally stood strictly for medium bombers, as distinguished from heavy bombers (HB) and light bombers (LB). In 1930, the USAAC decided that it made no sense to make such distinctions, and all of these categories were combined into one, B for bomber. There were already two entries in the B series, the Keystone XB-1B and the Curtiss B-2 Condor. Some of the LB bombers were reassigned new designations in the B-series. Subsequent designs were assigned bomber designations in the sequence in which they were ordered.
With the advent of missiles in the 1940s and 1950s, the USAF decided in 1951 to assign "B" designations to its ground attack missiles. The initial assignments were B-61 through B-65.
Here is the 1930-1962 B-series of Army/Air Force bombers:
1930-1962 Bomber Series
| Designation | Description |
| Keystone XB-1B | Originally was twin-engine adaptation of XHB-1 heavy bomber. Twin-rudder biplane. Two Curtiss V-1570 liquid-cooled engines. |
| Curtiss B-2 Condor | Twin-engined biplane bomber. Two Curtiss V-1570 liquid-cooled engines. 12 built. |
| Keystone B-3 | Twin-engine biplane bomber. Two P & W R-1690 radials. 36 built. |
| Keystone B-4 | Twin-engine biplane bomber. Two P & W R-1860 radials. 25 built. |
| Keystone B-5 | Twin-engine biplane bomber. Two Wright R-1750 radials. 27 built. |
| Keystone B-6 | Twin-engine biplane bomber. Two Wright R-1820 radials. 39 built. |
| Douglas YB-7 | Twin-engine monoplane bomber. Two Curtiss V-1570 liquid-cooled engines mounted under gull wings that were braced by metal struts. 7 built. |
| Fokker XB-8 | Twin-engine monoplane bomber. Adaptation of XO-27 long-range observation prototype. All-wood canti- lever wing, fabric-covered steel tube fuselage. Two Curtiss V-1570 liquid-cooled engines. Only one built. |
| Boeing Y1B-9 | Twin-engine monoplane bomber. Two P & W R-1860 radials. Crew of four in separate open cockpits. All-metal construction, retractable landing gear. Only 6 built. |
| Martin B-10 | Twin-engine monoplane bomber. Two Wright R-1820 radials. Enclosed cockpits, three 0.3 cal guns. First bomber with performance superior to contemporary fighters. |
| Douglas YB-11 | Twin-engine, long-range reconnaissance amphibian aircraft. Two Wright R-1820 radials mounted on pylons above the high-mounted wing. Retractable wheel undercarriage. Redesignated YO-44 and then YOA-5 before delivery to Army. |
| Martin YB-12 | Version of Martin bomber with P & W. R-1690 radials. 31 built. |
| Martin B-13 | Proposal to equip B-10 airframe with R-1860 radial engines. Cancelled before any could be delivered. |
| Martin XB-14 | B-10 airframe with 950hp R-1830 radials. Only one built. |
| Boeing XB-15 | Experimental four-engine long-range bomber. Only one built. Later converted into XC-105 cargoplane. |
| Martin XB-16 | Experimental six-engine long-range bomber. Six Allison V-1710 liquid-cooled engines, four as tractors, two as pushers. Two tail booms, twin rudders. Canceled before any could be built. |
| Boeing B-17 Fortress | Four-engine heavy bomber. Four Wright R-1820 Cyclone radials. Total of 12,677 built. |
| Douglas B-18 Bolo | Adaptation of DC-2 commercial transport to bombing role. |
| Douglas XB-19 | Four-engined long-range heavy bomber. Four Wright R-3350-5 radials. Only one built. |
| Boeing Y1B-20 | Proposed version of B-15 with 1400 hp Pratt and Whitney R-2180 radial engines. Two ordered. Canceled before any prototype could be completed. |
| North American XB-21 | Twin-engine medium bomber. Two P & W R-2180 Twin Hornets with superchargers. Crew of six. Five 0.30-cal guns in power turrets in nose and on top, and at mounts in waist and ventral positions. Only one built. |
| Douglas B-22 | Proposed adaptation of B-18 to take two Wright R-2600 radials. Cancelled in favor of B-23. |
| Douglas B-23 Dragon | Twin-engine medium bomber. Ordered as part of the B-18A contract. Embodied a greatly improved aerodynamic form and incorporated latest ideas on defensive armament, including a tail gun. Two Wright R-2600 Cyclones |
| Consolidated B-24 Liberator | Four-engine heavy bomber. Four Pratt and Whitney R-1830 radial engines on high-mounted wing. Total of 18,188 built, greater than that of any other American aircraft. |
| North American B-25 Mitchell | Twin-engine medium bomber. Two Wright R-2600 Cyclone radial engines. Total of 9816 built. |
| Martin B-26 Marauder | Twin-engine medium bomber. Two P & W R-2800 radials. High-mounted wing. Streamlined cigar-shaped fuselage Total of 5157 Marauders built. |
| Martin XB-27 | High-altitude adaptation of B-26. Two turbo- supercharged P & W R-2800 Wasps. Pressurized cabin. Project cancelled before any could be built. |
| North American XB-28 | High-altitude adaptation of B-25. Two turbo- supercharged P & W R-2800 Wasps. Pressurized cabin. Single rudder. No need was perceived for high- altitude medium bombers, and only two were built. |
| Boeing B-29 Superfortress | Long range, high altitude heavy bomber. Four Wright R-3350 radials. Unbroken nose, crew of 11, pressurized cabin. Four remote-controlled turrets, plus tail gun position. 3970 built |
| Lockheed XB-30 | Long range, high altitude bomber. Proposed bomber version of Constellation airliner. Entered in competition which eventually produced the B-29, but Lockheed withdrew from the contest before any prototypes could be built. |
| Douglas XB-31 | Long-range, high altitude bomber designed in competition with Boeing B-29. Canceled in favor of B-29 before any prototypes could be built. |
| Consolidated B-32 Dominator | High-altitude development of B-24. Four Wright R-3350 radials. Only 155 built. |
| Martin XB-33 | Long range bomber project with four 1800 hp R-2600 radials and twin tails. Canceled in favor of B-29 before it ever got off the drawing board. |
| Lockheed B-34 Ventura | Midwing twin-engine medium bomber with twin rudders. Military adaptation of Model 18 Lodestar airliner. |
| Northrop YB-35 | Long-range flying-wing bomber. Four P & W R-4360 radials with double turbosuperchargers driving pusher propellers. |
| Convair B-36 Peacemaker | Six-engine long-range heavy bomber. Six P & W R-4360 radials driving pusher props. D version had four General Electric J-47 jets in pods under outer wing to increase over-target speed. |
| Lockheed B-37 Ventura | Adaptation of B-34 Ventura for armed observation/ reconnaissance role with R-2600 engines. |
| Lockheed-Vega XB-38 | B-17E airframe converted by Vega division of Lockheed to take four Allison V-1710-89 liquid-cooled engines. Only one built. |
| Boeing XB-39 Superfortress | Conversion of B-29 airframe to take four Allison V-3420 liquid-cooled engines of 3000 hp. each. |
| Boeing YB-40 | Conversion of B-17F as escort fighter to improve defensive power of B-17 bomber formations. |
| Consolidated XB-41 | Escort fighter conversion of B-24D. Fourteen 0.50 cal guns. Only one built. |
| Douglas XB-42 | High-speed long-range medium bomber. Two Allison V-1710-125 water-cooled engines buried in fuselage driving pusher propellors behind the tail. Only two built. |
| Douglas XB-43 | First American jet bomber. XB-42 airframe fitted with two turbojets in forward fuselage bays fed by intakes located behind the cockpit. Lower tail fin eliminated, taller vertical tail. Two built. |
| Boeing XB-44 | B-29A with four P & W R-4360 radials in redesigned nacelles. Became prototype for B-29D which evolved into B-50. Three built. |
| North American B-45 Tornado | Four-jet medium bomber. First all-jet powered bomber to enter service with USAF. Four General Electric J-47 jets. |
| Convair XB-46 | Four-jet medium bomber. Four General Electric J-35 jets. 491 mph at sea level. Lost out to B-45 Tornado for production orders. |
| Boeing B-47 Stratojet | Six-jet swept-wing medium bomber. Six General Electric J-47 jets. 2041 built. Formed mainstay of American nuclear deterrent until 1966, when the last B-47E was retired. |
| Martin XB-48 | Six-jet medium bomber. Six Allison J-35 jets mounted three each in underwing pods. Only two built. |
| Northrop YB-49 | Conversion of B-35 to all-jet power. Eight Allison J-35 jets. Wing fences and vertical stabilizing fins were added. All turrets and guns were eliminated. Unstable and difficult to fly. Program was canceled in 1949 in favor of B-36. |
| Boeing B-50 Superfortress | Adaptation of B-29 to accommodate four P & W R-4360 radials of 3500 hp each housed in modified nacelles. Enlarged vertical tail.. 368 built. Many converted to training, reconnaissance, tanker, and weather research roles. |
| Martin XB-51 | Three-jet light bomber. Three General Electric J-47 jets, two under forward fuselage and one in tail. Lost out to B-57 in competition for production orders. |
| Boeing B-52 Stratofortress | Eight-jet long-range strategic bomber. Eight P & W J-57 engines mounted in four pods underneath swept- back wings Total of 744 built. |
| Convair XB-53 | Three-jet light bomber project. Canard design with swept-forward wing. Three J-35 jets. Was formerly XA-44. Canceled before completion. |
| Boeing XB-54 | Proposed version of B-50 with P & W R-4360-51 compound engines. Canceled in favor of B-36 before any prototype could be completed. |
| Boeing XB-55 | Long-range heavy bomber powered by four Allison T-40 turboprops housed in pods under a slightly swept- back wing. Abandoned before prototype could be completed because of greater promise of B-52. |
| Boeing XB-56 | Version of B-47 with four Allison J-71 jets. Project was canceled before prototype could be completed. |
| Martin B-57 Canberra | American-built version of English Electric Canberra twin-jet light bomber. Total of 403 built. High-altitude reconnaissance and target towing versions also built. |
| Convair B-58 Hustler | Four-engine supersonic medium bomber. Four General Electric J-79 jets with afterburners in individual pods under a delta wing. Total of 116 built |
| Boeing XB-59 | Supersonic bomber project powered by four General Electric J-73 engines. Lost out to Convair B-58 for Air Force orders. Never got off the drawing board. |
| Convair YB-60 | Jet-powered version of B-36. Eight J-57 jets, swept wing and tail. Only two built. |
| Martin B-61 Matador | Single-engine ground-launched cruise missile. Later redesignated TM-61 and later MGM-1 |
| Northrop B-62 Snark | Single-engine ground-launched strategic cruise missile. Later redesignated SM-62. |
| Bell B-63 Rascal | Air-launched strategic missile. Later redesignated GAM-63 |
| North American B-64 Navajo | Ground-launched strategic supersonic cruise missile. Later redesignated SM-64. |
| Convair B-65 Atlas | Ground-launched intercontinental ballistic missile. Later redesignated SM-65 and later PGM-16/CGM-16/HGM-16 |
| Douglas B-66 Destroyer | Air Force adaptation of carrier-based A3D Skywarrior light bomber. Two Allison J-71 jets. Bomber, reconnaissance, and electronic countermeasures versions produced. Total of 294 built. |
| Radioplane B-67 Crossbow | Decoy missile. Designation later changed to GAM-67 |
| Martin XB-68 | Two-seat tactical bomber powered by two P & W J-75 engines. High T-tail and rotary bomb door. Canceled in 1957. |
| Lockheed B-69 Neptune | Designation allocated to seven P2V-7U Neptune patrol planes ordered from the Navy for special electronic intelligence missions. |
| North American XB-70A Valkyrie | Mach 3 strategic bomber. Six General Electric J-93 engines. Delta wing. Twin rudders. Only two prototypes built. |
| B-71 | Number used for Lockheed SR-71 twin-engined Mach 3+ strategic reconnaissance aircraft. |
Post-1955 Missile Designations
| Designation | Description |
| Radioplane GAM-67 Crossbow | Decoy missile |
| Martin SM-68 Titan | Two-stage intercontinental ballistic missile. Later redesignated HGM-25/LGM-25. |
| M-69 | Allocate briefly in 1955 for redesignation of F-99 Bomarc. Later changed to IM-99 |
| Bendix IM-70 Talos | Talos land-based weapons system. |
| Convair XGAM-71 Buck Duck | Air-launched decoy missile for B-36, about which very little is known. |
| McDonnell GAM-72 Green Quail | Air-launched decoy missile. Some sources have this as having Been originally designated B-72. Name later shortened to Quail |
| Fairchild SM-73 Bull Goose | Surface to Surface missile. Name later shortened to Goose. |
| M-74 | Allocated to Convair-designed long range decoy misssile whjich lost out to th Fairchild SM-73 |
| Douglas SM-75 Thor | Single-stage surface-to-surface intermediate ballistic missile. Later redesignated PGM-17. |
| Martin TM-76 Mace | Jet-powered surface to surface cruise missile. Later redesignated CGM-13. |
| North American GAM-77 Hound Dog | Jet-powered air to surface missile. Later redesignated AGM-28. |
| Chrysler SM-78 Jupiter | Single-stage surface-to-surface intermediate-range ballistic missile. Later redesignated PGM-19. |
| Martin GAM-79 White Lance | Project which ultimately led to the development of the Air Force version of the GAM-83 Bullpup. |
| Boeing SM-80 Minuteman | Two-stage surface-to-surface intercontinental ballistic missile. Later redesignated LGM-30 |
| Lockheed RM-81 Agena | Designation associated with the Agena upper-stage space launcher. |
| JPL XRM-82 Loki-Dart | Single-stage sounding rocket. Redesignated PWN-1A in 1963 |
| Martin GAM-83 Bullpup | Air to surface missile. Later redesignated AGM-12. |
| Aerojet General XRM-84 Aerobee-Hi | Two stage sounding rocket. Redesignated PWN-2A in 1963 |
| Univ. of Michigan/NASA XRM-85 Nike-Cajun | Two-stage sounding rocket. Redesignated PWN-3A in 1963. |
| Univ. of Michigan XRM-86 Exos | Three-stage sounding rocket. Redesignated PWN-4A in 1963. |
| Douglas GAM-87 Skybolt | Air to surface ballistic missile. Later redesignated AGM-48. |
| Cooper SRM-88 Rocksonde 200 | Single-stage sounding rocket. Later redesignated PWN-5A. |
| Ford XRM-89 Blue Scout 1 | 3-stage missile based on NASA Scout used for suborbital tests. |
| Ford XRM-90 Blue Scout 2 | Similar to Blue Scout 1 but with added fourth stage. Used for suborbital and orbital tests. |
| Ford XRM-91 Blue Scout Junior | Smaller Air Force version of Scout used for suborbital military tests. Second and third stages of Blue Scout 2 used for first two stages. |
| Ford XRM-92 Air Force Scout | Four-stage rocket similar to the original NASA Scout. |
In 1935, there was a relatively short-lived category introduced, known as Bomber, Long Range, or BLR. There were only three entries:
Boeing BLR-1 Experimental four-engine long-range bomber. Redesignated XB-15 in 1936 Douglas BLR-2 Experimental four-engine long range bomber. Redesignated XB-19 in 1936. Sikorsky BLR-3 Experimental long-range bomber. Project abandoned before anything could be built.
In 1936, the BLR category was eliminated, and the two flying examples were redesignated B-15 and B-19 respectively.
In 1962, the Defense Department decided to restart the B-series bomber designations over again from 1. The designations of the bombers already in
service in 1962, however, were unchanged. Here is the new B-series of bombers.
So far, there are only two entries.
Rockwell B-1B Lancer Four-engine variable sweep strategic bomber and cruise missile carrier. Total of 100 built. Northrop B-2 Spirit Two-seat, four-engine low-observable multi-role bomber. Northrop Grumman B-21 Raider Under development for the USAF by Northrop Grumman. The bomber is expected to enter service by 2025. It is to complement existing Rockwell B-1 Lancer, Northrop Grumman B-2 Spirit, and Boeing B-52 Stratofortress bomber fleets in U.S. service and eventually replace these bombers
