Boeing B-17 Flying Fortress Four-engine heavy bomber. Four Wright R-1820 Cyclone radials. Production severely cut back in wake of 1940 decision to concentrate on bombers with transoceanic range
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. Small number (circa 20) built as TB-19 to provide interim trainers and cadre aircraft prior to availability of B-36
Boeing YB-20 Experimental four-engine long-range bomber. Only one built. Proposed version with 1400 hp Pratt and Whitney R-2180 radial engines 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 XB-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.
Consolidated XB-24 Liberator Four-engine heavy bomber. Four Pratt and Whitney R-1830 radial engines on high-mounted wing. One prototype built, production order cancelled.
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
Martin B-27 Super-Marauder High-altitude adaptation of B-26. Two turbo- supercharged P & W R-2800 Wasps. Pressurized cabin. Replaced B-25 and B-26 from 1945 onwards. Also supplied to Russia under lend-lease. Served until early 1950s. Many supplied to other countries most notably India. Last examples not withdrawn from non-US service until early 1970s.
North American XB-28 Hillbilly High-altitude adaptation of B-25. Two turbo- supercharged P & W R-2800 Wasps. Pressurized cabin. Single rudder. Cancelled in favor of B-27 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. Planned production cut back dramatically in favor of B-36.
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 XB-32 Dominator Proposed long-range bomber, cancelled to allow Convair to concentrate on B-36.
Martin B-33 Long range bomber project with four 1800 hp R-2600 radials and twin tails. Cancelled due to poor performance but redesigned as a short-range heavy bomber intended to replace the B-17 in interdiction and tactical support roles. Single tail, powered by four R-2800s. Production was limited due to the Martin plants being swamped by production of B-26 and B-27 aircraft.
Lockheed B-34 Ventura Midwing twin-engine medium bomber with twin rudders. Military adaptation of Model 18 Lodestar airliner. Limited production in early 1940s mostly assigned to Navy for ASW patrols
Northrop YB-35 Long-range flying-wing bomber competitor to B-36. Four P & W R-4360 radials with double turbosuperchargers driving pusher propellers. Cancelled due to technical problems, excessive cost and poor performance.
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. Primary striking force of US SAC from 1944 to 1956. More than 6,000 built. Remained in service until 1958.
Lockheed B-37 Ventura Adaptation of B-34 Ventura for ASW 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 following massive B-29 losses in 1944/45 bombing raids. Cancelled due to inadequate range/speed/altitude profile.
Boeing YB-40 Conversion of B-17E as escort bomber to improve defensive power of B-17 bomber formations.
Boeing YB-41 Escort bomber conversion of B-29. Eighteen 0.50 cal guns. Small number built, has unique distinction of entire production run being shot down by enemy fighters.
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-50. Three built.
North American B-45 Tornado Four-jet medium bomber. First all-jet powered bomber to enter service with USAF. The B-45 entered service in 1948 and was phased out by the early 1950s. It was just a little too late to see service in WW2 and it was a casualty of the general decline of tactical aviation in the 1950s. The survivors were operated briefly by NORAD and were replaced by F-100s. 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 primarily to avoid interrupting B-36 production
Boeing XB-47 Stratojet Proposed six-jet swept-wing medium bomber. Six General Electric J-47 jets. Never used by air force but 500 built for Navy as land-based maritime bombers under designation PB2B-2 Sinatra
Martin XB-48 Six-jet medium bomber. Six Allison J-35 jets mounted three each in underwing pods. Cancelled in favor of B-47 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. Complete technical failure, expensive, unstable and difficult to fly. Program was canceled in 1949 in favor of further production of B-36.
Boeing XB-50 Superfortress Proposed adaptation of B-29 to accommodate four P & W R-4360 radials of 3500 hp each housed in modified nacelles. Enlarged vertical tail. Cancelled due to lack of operational requirement but design was licensed to Tupolev Design Bureau who built over 1,000 as Tu-4. These served with Russian long-range aviation and naval aviation.
Martin XB-51 Three-jet light bomber. Three General Electric J-47 jets, two under forward fuselage and one in tail. Cancelled due to lack of operational requirement
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 3744 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-29 with P & W R-4360-51 compound engines. Canceled in favor of B-36 before any prototype could be completed. One built in Russia as Tu-8 but cancelled in favor of turboprop powered Tu-95
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. ASW development offered to Navy but declined in favor of P3V
Boeing XB-56 Version of B-47 with four Allison J-71 jets. Project was canceled before prototype could be completed. Offered to Navy, declined in favor of PB5Y version of B-58
Martin XB-57 Twin-jet light bomber to replace B-45. Never built due to lack of operational requirement.
Convair RB-58 Hustler Four-engine supersonic strategic reconnaissance bomber replacing RB-36 and RB-52. Four General Electric J-79 jets with afterburners in individual pods under a delta wing on RB-58A to RB-58D. Four unreheated J-58s on RB-58E to RB-58K
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 B-60 Devastator Jet-powered version of B-36. Eight J-57 jets, swept wing and tail. Withdrawn from nuclear strike role by 1960 but served as conventional bomber for SAC until early-1970s.
Martin XB-61 Matador Single-engine ground-launched cruise missile. Cancelled in 1957 "Missile Massacre"
Northrop XB-62 Snark Single-engine ground-launched strategic cruise missile. The discovery that one of these missiles fired on a test had hit the wrong continent sparked off the 1957 "Missile Massacre". Cancelled in 1957
Bell XB-63 Rascal Air-launched strategic missile. Cancelled in 1957 "Missile Massacre"
North American XB-64 Navajo Ground-launched strategic supersonic cruise missile. Cancelled in 1957 "Missile Massacre"
Convair XB-65 Atlas Ground-launched intercontinental ballistic missile. Cancelled in 1957 "Missile Massacre" but subsequently developed as satellite booster.
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 but the B-66 program was a casualty of the general decline of tactical aviation in the 1950s. The small force was operated by NORAD. Total of 294 built.
Martin XB-67 Titan Ground-launched intercontinental ballistic missile. Cancelled in 1957 "Missile Massacre" but subsequently developed as satellite booster.
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 in favor of F-105.
Boeing XB-69 Minuteman Ground-launched intercontinental ballistic missile. Cancelled in 1957 "Missile Massacre"
North American B-70 Valkyrie Mach 3 strategic bomber. Six General Electric J-93 engines. Delta wing. Twin rudders. Mainstay of SAC bomber groups until early 21st century. Over 3,000 built
Lockheed B-71 Blackbird Light bomber version of Lockheed SR-71 and RS-71 twin-engined Mach 3+ strategic reconnaissance aircraft. Became part of “Air Commando” units responsible for finding and destroying mobile strategic targets.
Douglas XB-72 Thor Intermediate range ballistic missile Cancelled in 1957 "Missile Massacre"
Martin XB-73 Titan II Ground-launched intercontinental ballistic missile. Proposed development of XB-67 Cancelled in 1957 "Missile Massacre" but subsequently developed as satellite booster.
Convair B-74 Dominator Very large six-engined conventional bomber replacing B-60. Not assigned nuclear delivery roles. Remained in limited service until around 2010
Boeing XB-75 Minuteman II Proposed ground-launched intercontinental ballistic missile development of XB-69. Cancelled in 1957 "Missile Massacre"
Lockheed XB-76 Polaris Proposed sea launched ballistic missile being developed for US Navy. Reason for designation in USAF bomber sequence is unknown. Cancelled in 1957 "Missile Massacre"
North American B-77 Hound Dog Long-range stand-off missile deployed on B-52B to B-52G
Chrysler XB-78 Jupiter Joint Army/Air Force intermediate range ballistic missile. Cancelled in 1957 "Missile Massacre" but subsequently developed as satellite booster.
Martin B-79 White Lance Long-range stand off cruise missile deployed on RB-58
Boeing XB-80 Minuteman III Concept design for ultimate ground-launched intercontinental ballistic missile development of XB-69. Cancelled in 1957 "Missile Massacre"
Lockheed B-81 Agena Air-launched ballistic missile carried in bomb bay of B-52D – G
Martin XB-82 Lone Star Competitor to B-81. Cancelled.
Teledyne B-83 Quail Decoy missile deployed on B-52
Teledyne B-84 Grouse Decoy missile deployed on B-58
Teledyne B-85 Pigeon Decoy missile deployed on B-70 and B-71
Douglas B-87 Skybolt Air-launched ballistic missile deployed on B-52
Convair XB-88 Proposed development of B-74 Dominator. Cancelled.
Thiokol B-89 Short range attack missile used on B-52, B-58, B-70 and B-71.
Convair B-90 Airhawk Long range air-launched cruise missile
Note. Designations B-91 to B-99 apparently not used. May refer to proposed variants developed from Dyna-Soar program
North American YGB-100 Large mothership aircraft derived from B-70 Valkyrie, intended as re-usable first stage of surface-to-space (aerospace) fighters and bombers until multi-mode engines perfected.
Boeing B-100 Dynasoar Manned orbital strategic bomber. Surface-based using YGB-100 manned first stage or based on Manned Orbiting Weapons System (MOWS Space Station)
North American XB-101 Robo Manned orbital strategic bomber and space exploration craft. Surface-based using YGB-100 manned first stage or based on Manned Orbiting Weapons System (MOWS Space Station)
North American B-101A Robo. Despite similarity of designation, had only marginally commonality with XB-101. Powered by four turboscramrockets to give single stage to orbit. First flew 1989 but lengthy technical development delayed service entry until 2001.
North American B-103 Valkyrie. Highly developed version of B-70 Valkyrie with turboscramjets based on J-93 engines. First entered service 1998. Replacing B-70 in squadron service.
Lockheed-Boeing RB-104 Vulture. Turboscramrocket single-stage-to-orbit bomber to replace RB-58 series. Started entering service 1998
Bell-Martin GRB-105 Phoenix Manned orbital strategic reconnaissance and space exploration craft based on Dynasoar. Surface-based using YGB-100 manned first stage or based on Manned Orbiting Weapons System (MOWS Space Station). Limited replacement for SR-71 aircraft. Entered service in 1985, replaced from 2000 onwards by RB-107
North American B-106 Aurora Developed single-stage to orbit version of the B-103 with turboscramrockets giving it sub-orbital attack capability. Entering service 2006.
Bell-Martin RB-107 Phoenix Advanced derivative of the GRB-105 equipped with Turboscramrockets to give single stage to orbit capability. Replaced GRB-105, SR-71 and RS-71 aircraft from 2000.