Designations Of U.S. Nuclear Weapons
Copyright © 20012005 Andreas Parsch
3 Sources
All U.S. nuclear weapons (missile warheads, freefall bombs, artillery shells, etc.) are numbered in a single, consecutive series. The numbers are assigned by the organization controlling the design and manufacture of nuclear weapons. From 1946 to 1974, this was the Atomic Energy Commission (AEC). In 1974, the AEC was abolished and its tasks being taken over by the newly formed Energy Research and Development Administration (ERDA). In 1977, the Department of Energy (DOE) was founded and took over, among many other things, the responsibility for nuclear weapons.
When designating nuclear weapons, a variety of prefixes and suffixes are used with the numbers. However, I don't have any official, firsthand source describing or regulating their use. The following prefixes were used at least once:
The first four designs used roman numerals, but this was soon changed to arabic numerals with the MKIV/MK4. A dash is usually written between the prefix and the number. In newer references, however, the dash is frequently omitted. Especially the reference to bombs as Bn instead of Bn is quite common, presumably to avoid confusion with US Air Force bomber designations. The warhead (i.e. the nuclear package) of a freefall bomb always retained its W designation, using the same number as the bomb itself. E.g. the nuclear components of the MK28 bomb were known as W28 (in the strictest sense, the MK nomenclature applied only to the nonnuclear bomb components).
Suffixes are used to designate variants of a weapon. The basic suffix is a "Mod" designator. This is used in the same way as in the US Navy's MARK/MOD Nomenclature System, i.e. the first version is designated "Mod 0", followed by "Mod 1", etc. The Mod suffix is often abbreviated to a dash and a number, e.g. B6111 or W801. Different yield options for a weapon can be indicated by a Yn (n = 1, 2, ...) designator immediately behind the number. Of course, Y and Mod suffixes can be combined, as in W39Y1 Mod 2. Modifications of bomb and warhead prototypes were often indicated by a Xn (n = 1, 2, ...) suffix, as in TX7X1. If an Xn design was put into production, the Xn usually became a Mod number (e.g. TX7X1 became MK7 Mod 1).
The list includes every nuclear weapon which was ever assigned a number in the AEC/DOE series. Warheads are always listed as Wn, but bombs are generally shown with the most "common" prefix. All warheads had XW or TX designations when the number was first assigned. Similarly, most bombs started as TX designs before being designated as MK, B or EC.
For each weapon, the developing laboratory (LANL = Los Alamos National Laboratory, LLNL = Lawrence Livermore National Laboratory), the approximate yield(s) and the delivery platforms (carrier aircraft for bombs, missiles for warheads) are listed. Brackets indicate cancelled bombs, warheads and platform/warhead combinations.
Most rockets and missile designations are linked to the corresponding page in the Directory of U.S. Military Rockets and Missiles, which includes detailed information about the weapon.
Number  Laboratory  Yield  Platforms  Remarks 
MKI  LANL  15 kT  B29 Superfortress  "Little Boy" (dropped on Hiroshima) was a MKI type bomb 
[MKII]  LANL  Design similar to "Fat Man"; not developed  
MKIII  LANL  18 kT  49 kT 
B29 Superfortress B50A/D Superfortress 
"Fat Man" (dropped on Nagasaki) was a MKIII type bomb 
MKIV/MK4 [W4] 
LANL  1 kT  31 kT 
MK4 Bomb: B29 Superfortress B36 Peacemaker B50A/D Superfortress AJ, A2 Savage W4 Warhead: [B62, SM62 Snark] [B64, SM64 Navaho] 
Derived from MKIII Mod 1; W4 missile warhead cancelled in favour of W13 
MK5 W5 
LANL  11 kT  47 kT 
MK5 Bomb: B29 Superfortress B36 Peacemaker B45A Tornado B47A/B/E Stratojet B50A/D Superfortress B66 Destroyer AJ, A2 Savage A3D1/2, A3A/B Skywarrior W5 Warhead: B61, TM61A/C, MGM1C Matador SSMN8a, RGM6B Regulus [B63, GAM63 Rascal] [SSMN2 Triton] [SSMN6 Rigel] [SSMA16 Hermes A3B] 
XW5 for GAM63 was cancelled in favour of W27 
MK6  LANL  8 kT  160 kT 
B29 Superfortress B36 Peacemaker B47A/B/E Stratojet B50A/D Superfortress B66 Destroyer AJ, A2 Savage A3D1, A3A Skywarrior 
Improved MK4; some retired MK6 bombs were converted into "Project A" ADM (ADMA) 
MK7 W7 
LANL 
MK7: 8 kT  61 kT W7: 90 T, 2  40 kT 
MK7 Bomb: B45A Tornado B57B Intruder F84E/F/G Thunderjet/Thunderstreak F100D/F Super Sabre F101A/C Voodoo AD4B Skyraider AJ, A2 Savage A3D1, A3A Skywarrior A4D2/5, A4B/C/E/J/M Skyhawk FJ4B, AF1E Fury F2H2B Banshee F3H2N, F3C Demon F9F8B, AF9J Cougar W7 Warhead: 30.5" Rocket MK 1 MOD 0 BOAR SSMA17, M2, MGM5A/B Corporal M31/M50, MGR1A/B/C Honest John "Project B" ADM (ADMB) MK 90 Betty ASW Bomb [GAM67 Crossbow] [SSMA13 Hermes A2] [SAMA25, M6, MIM14 Nike Hercules] 
MK7 was nicknamed "Thor"; XW7 for GAM67 and MIM14 was cancelled in favour of W31 
MK8 [W8] 
LANL  25 kT  30 kT 
MK8 Bomb: B45A Tornado AD4B Skyraider AJ, A2 Savage A3D1, A3A Skywarrior A4D2/5, A4B/C/E/J/M Skyhawk F2H2B Banshee F3H2N, F3C Demon W8 Warhead: [SSMN8, RGM6 Regulus] 
MK8 was nicknamed "Elsie" (for "LC": Light Case); replaced by MK11 
W9  LANL  15 kT 
T124 280 mm Artillery Shell T4 ADM 

[TX10] [W10] 
LANL  12 kT  15 kT 
W10 Warhead: [KGW1 Loon] 
TX10 was to be an airburst derivative of the MK8 
TX11 (MK91)  LANL  30 kT (?) 
AD4B/7, A1J Skyraider AJ, A2 Savage A3D1, A3A Skywarrior A4D2/5, A4B/C/E/J/M Skyhawk F2H2B Banshee F3H2N, F3C Demon 
Improved MK8; MK11 production version was known as MK91 Mod 0 bomb 
MK12 [W12] 
LANL  12 kT, 14 kT 
MK12 Bomb: F86F/H Sabre AD6/7, A1H/J Skyraider AJ, A2 Savage A3D1, A3A Skywarrior A4D2/5, A4B/C/E/J/M Skyhawk FJ4B, AF1E Fury F2H2B Banshee F3H2N, F3C Demon F9F8B, AF9J Cougar W12 Warhead: [SAMN6, IM70, RIM8 Talos] [30.5" Rocket MK 1 MOD 0 BOAR] 
MK12 was nicknamed "Brok"; W12 was cancelled in favour of W7 (BOAR) and W30 (Talos) 
[TX13] [W13] 
LANL  32 kT 
W13 Warhead: [B62, SM62 Snark] [B64, SM64 Navaho] [SSMA14, M8, PGM11 Redstone] 
W13 was cancelled in favour of W15 and later W39 
EC14  LANL  5 MT  7 MT  B36 Peacemaker  
MK15 [W15] 
LANL  1.7 MT, 3.4 MT 
MK15 Bomb: B36 Peacemaker B47B/E Stratojet B52 Stratofortress A3D1, A3A Skywarrior W15 Warhead: [B62, SM62 Snark] [B64, SM64 Navaho] [SSMA14, M8, PGM11 Redstone] 
W15 was cancelled in favour of W39 
[TX16]  LANL  6 MT  8 MT  
MK17  LANL  15 MT  20 MT  B36 Peacemaker  
MK18  LANL  500 kT 
B36 Peacemaker B47A/B/E Stratojet A3D1, A3A Skywarrior 

S19  LANL  15 kT  T315 280 mm Artillery Shell  
[TX20]  LANL  Proposed highyield derivative of MK13  
MK21 [W21] 
LANL  4 MT  5 MT 
MK21 Bomb: B36 Peacemaker B47B/E Stratojet B52 Stratofortress W21 Warhead: [B64, SM64 Navaho] 
Later converted to MK36 
[TX22]  LLNL  Design cancelled after preliminary test failure  
S23  LANL  15 kT  20 kT  16" Shipborne Gun Shell  A 280 mm shell warhead incorporated into a bigger shellcase for the 16" guns 
MK24  LANL  15 MT  20 MT  B36 Peacemaker  Very similar to MK17 
W25  LANL  1.7 kT 
MB1, AIR2A Genie [M51, MGR3 Little John] ["Project C" ADM (ADMC)] 

[TX26]  LANL  Cancelled derivative of MK21  
MK27 W27 
LLNL  2 MT 
MK27 Bomb: AJ, A2 Savage A3D1/2, A3A/B Skywarrior A3J1, A5A Vigilante W27 Warhead: SSMN8a, RGM6B Regulus [B61, TM61, MGM1 Matador] [B63, GAM63 Rascal] [SSMN2 Triton] [SSMN9, RGM15 Regulus II] 

MK28 W28 
LANL 
MK28: 70 kT (Y1), 350 kT (Y2), 1.1 MT (Y3), 1.45 MT (Y5) W28: 11 kT  1.1 MT 
MK28 Bomb: B47B/E Stratojet B52 Stratofortress B66 Destroyer F100D/F Super Sabre F101A/C Voodoo F104C/G Starfighter F105 Thunderchief F/FB111 Aardvark F4C/D/E Phantom II A3D1/2, A3A/B Skywarrior A4D2/5, A4B/C/E/J/M Skyhawk A3J1, A5A Vigilante A2F, A6 Intruder A7 Corsair II FJ4B, AF1E Fury W28 Warhead: TM76A/B, MGM/CGM13A/B Mace GAM77/A, AGM28A/B Hound Dog 
Used W34 "Python" as fission primary 
[W29]  LANL 
[B64, SM64 Navaho] [SSMA14, M8, PGM11 Redstone] 
Modified W15; cancelled in favour of W39  
W30  LANL  0.5 kT, 2 kT 
SAMN6bW/bW1/c1, RIM8B/D/E Talos XM113 TADM [F99, IM99, CIM10 Bomarc] [AIM68 Big Q] 
Used as "Boa" fission primary in W52; W30/Bomarc cancelled in favour of W40 
W31  LANL 
2 kT, 20 kT, 40 kT (MGR1) 1 kT  2 kT, 30 kT  40 kT (MIM14) 1 kT  40 kT (ADM) 
M31/M50, MGR1A/B/C Honest John (Y3) SAMA25, M6, MIM14A/B/C Nike Hercules (Y1, Y2) ADM [GAM67 Crossbow] 

[S32]  LANL  [T332 240 mm Artillery Shell]  Cancelled in favour of W48  
W33  LANL  5 kT  40 kT  M422 8" Artillery Shell  
W34  LANL  11 kT 
MK 101 Lulu NDB (Nuclear Depth Bomb) MK 105 Hotpoint Bomb MK 45 ASTOR Torpedo 
Nicknamed "Python"; also used as gasboosted fission primary in W28, W40 and W49 
[W35]  LANL  1.75 MT 
[SM65D/E/F, CGM/HGM16D/E/F Atlas] [SM68, HGM25A Titan] [SM75, PGM17 Thor] [SM78, PGM19 Jupiter] 
Cancelled in favour of W38 (Atlas E/F, Titan) and W49 (Atlas D, Thor, Jupiter) 
MK36  LANL  10 MT 
B36 Peacemaker B47B/E Stratojet B52 Stratofortress 

[W37]  LANL  [SAMA25, M6, MIM14 Nike Hercules]  XW37 was redesignated XW31Y2  
W38  LLNL  4.5 MT 
SM65E/F, CGM16E/F Atlas SM68, HGM25A Titan 
Used "Robin" (see W48) as fission primary 
MK39 W39 
LLNL  3 MT  4 MT 
MK39 Bomb: B36 Peacemaker B47B/E Stratojet B52 Stratofortress B58 Hustler (BA39 in bomb pod) A3D1, A3A Skywarrior W39 Warhead: B62, SM62A Snark SSMA14, M8, PGM11A Redstone [B64, SM64 Navaho] 

W40  LANL 
7 kT  10 kT (CIM10) 1.7 kT, 10 kT (MGM18) 
F99, IM99A/B, CIM10A/B Bomarc SSMA12, M4, MGM18A Lacrosse [ASMN8 Corvus] 
Used W34 "Python" as fission primary 
MK41 [W41] 
LLNL  25 MT 
MK41 Bomb: B47B/E Stratojet B52 Stratofortress 

[W42]  LLNL 
[GAR9, AIM47 Falcon] [AAMN9 Sparrow X] [AAMN10 Eagle] [SAMA18, M3, MIM23 Hawk] 
Cancelled in favour of W54  
MK43  LANL  70 kT, 500 kT, 1 MT 
B47B/E Stratojet B52 Stratofortress B57B Intruder B58 Hustler F100D/F Super Sabre F101A/C Voodoo F104C/G Starfighter F105 Thunderchief F/FB111 Aardvark F4C/D/E Phantom II A3D1/2, A3A/B Skywarrior A4D2/5, A4B/C/E/J/M Skyhawk A3J1, A5A Vigilante A2F, A6 Intruder A7 Corsair II FJ4B, AF1E Fury 
Used W44 "Tsetse" as fission primary 
W44  LANL  300 T, 10 kT  RUR5A Asroc  Nicknamed "Tsetse"; also used as fission primary in MK43, W50, MK57 and W59 
W45  LLNL  500 T  15 kT 
GAM83B, AGM12D Bullpup (Y3, Y4) SAMN7, RIM2D Terrier (Y1, Y4) M51, MGR3A Little John (Y1, Y2, Y4) MADM (Y1, Y2, Y3, Y4) 
Used "Robin" (see W48) as fission primary 
[TX46] [W46] 
LANL  10 MT 
W46 Warhead: [SSMA14, M8, PGM11 Redstone] 
Cancelled in favour of MK53/W53 
W47  LLNL  600 kT (Y1), 1.2 MT (Y2)  UGM27A/B Polaris A1/A2  Used "Robin" (see W48) as fission primary 
W48  LLNL  70 T  100 T  M454 155 mm Artillery Shell  Unboosted derivative of "Robin" fission primary of W38, W45 and W47 
W49  LANL  1.45 MT 
SM65D, PGM16D Atlas SM75, PGM17A Thor SM78, PGM19A Jupiter 
Used W34 "Python" as fission primary 
W50  LANL  60 kT (Y1), 200 kT (Y2), 400 kT (Y3) 
M14, MGM31A/B Pershing XLIM49A Nike Zeus B [HSM80A, LGM30A Minuteman] [ASMNx Hopi] 
Used W44 "Tsetse" as fission primary 
[W51]  LLNL  22 T 
[GAR11, AIM26 Falcon] [M388 Projectile for M28/M29 Davy Crockett] 
XW51 was transferred to LANL and redesignated XW54 
W52  LANL  200 kT  SSMA27, M15, MGM29A Sergeant  Used "Boa" (see W30) as fission primary 
MK53 W53 
LANL  9 MT  10 MT 
MK53 Bomb: B47B/E Stratojet B52 Stratofortress B58 Hustler (BA53Y1 in BLU2/B pod) W53 Warhead: SM68B, LGM25C Titan II 

W54  LANL 
250 T (GAR11) 10 T, 20 T (M388) 10 T  1 kT (SADM) 
GAR11, AIM26A Falcon M388 Projectile for M28/M29 Davy Crockett M129/M159 SADM 
SADM (Special Atomic Demolition Munition) was also known as B54 
W55  LLNL  250 kT  UUM44A Subroc  Used "Kinglet" fission primary; some sources erroneously quote a low kiloton yield (1  5 kT) 
W56  LLNL  1.2 MT  HSM80B/F, LGM30B/F Minuteman I/II (Mk.11 RV)  Nicknamed "Fife"; design based on W47 
MK57  LANL  5 kT  20 kT 
B52 Stratofortress F100D/F Super Sabre F104C/G Starfighter F105 Thunderchief F/FB111 Aardvark F4C/D/E Phantom II A3D2, A3B Skywarrior A4D2/5, A4B/C/E/J/M Skyhawk A3J1, A5A Vigilante A2F, A6 Intruder A7 Corsair II F/A18 Hornet P2V5F/7, P2E/H Neptune P3 Orion S2F1/2/3/3S, S2A/C/D/E Tracker S3 Viking SH3D/H Sea King 
Used W44 "Tsetse" as fission primary 
W58  LLNL  200 kT  UGM27C Polaris A3  Used "Kinglet" fission primary (see W55) 
W59  LANL  800 kT, 1.2 MT 
HSM80A, LGM30A Minuteman I (Mk.5 RV) [GAM87, AGM48 Skybolt] 
Used W44 "Tsetse" as fission primary 
[W60]  LLNL  (low)  [SAMN8, RIM50 Typhon LR]  
B61  LANL 
10 kT  300 kT (Mod 0/1/7) 10 kT  150 kT (Mod 2/5) 300 T, 1.5 kT, 60 kT, 170 kT (Mod 3) 300 T, 1.5 kT, 10 kT, 45 kT (Mod 4) 300 T, 5 kT, 10 kT, 80 kT (Mod 10) 1.7 kT  300 kT (Mod 11) 
B52 Stratofortress B1B Lancer B2A Spirit F100D/F Super Sabre F104C/G Starfighter F105 Thunderchief F/FB111 Aardvark F117A Nighthawk F4C/D/E Phantom II F15E Eagle F16 Fighting Falcon A4D2/5, A4B/C/E/J/M Skyhawk A2F, A6 Intruder A7 Corsair II F/A18 Hornet 
Also known as MK/B61 
W62  LLNL  170 kT 
LGM30G Minuteman III (Mk.12 RV) [UGM73 Poseidon C3] 
W62/Poseidon was cancelled in favour of W68 
[W63]  LLNL  [MGM52 Lance]  Enhanced Radiation ("Neutron Bomb") warhead; cancelled in favour of W70  
[W64]  LANL  [MGM52 Lance]  Enhanced Radiation ("Neutron Bomb") warhead; cancelled in favour of W63  
[W65]  LLNL  [LIM100(?) Sprint]  Enhanced Radiation ("Neutron Bomb") warhead; cancelled in favour of W66  
W66  LANL  1 kT  LIM100(?) Sprint  Enhanced Radiation ("Neutron Bomb") warhead 
[W67]  LANL  150 kT 
[LGM30G Minuteman III] [UGM73 Poseidon] 
Cancelled in favour of W62 (Minuteman) and W68 (Poseidon) 
W68  LLNL  40 kT  50 kT  UGM73A Poseidon C3  
W69  LANL  170 kT  200 kT  AGM69A SRAM  
W70  LLNL  1 kT  100 kT (Mod 0/1/2) 1 kT (Mod 3) 
MGM52C Lance  Mod 3 is the Enhanced Radiation ("Neutron Bomb") version 
W71  LLNL  5 MT  LIM49A Spartan  
W72  LANL  625 T  AGM62 Walleye MK 6 MOD 0  Modified from retired W54 warheads 
[W73]  LANL  [ASMN11, AGM53A Condor]  Derived from MK/B61  
[W74]  LANL  > 100 T  [155 mm Artillery Shell]  Cancelled in favour of W82 
[W75]  LLNL  > 100 T  [8" Artillery Shell]  Similar to W74; cancelled in favour of W79 
W76  LANL  90 kT  100 kT  UGM96A Trident  
[B77]  LLNL  1 MT  Cancelled in favour of B83  
W78  LANL  335 kT  350 kT  LGM30G Minuteman III (Mk.12A RV)  Derived from W50 
W79  LLNL 
100 T  1.1 kT (Mod 0) 100 T  0.8 kT (Mod 1) 
XM753 8" Artillery Shell  Mod 1 has Enhanced Radiation ("Neutron Bomb") option 
W80  LANL 
5 kT  200 kT (W800) 5 kT  150 kT (W801) 
BGM/RGM/UGM109A Tomahawk (W800) AGM86B ALCM (W801) AGM129A ACM (W801) 
Derived from MK/B61 
[W81]  LANL  3 kT  4 kT  [RIM67 Standard SM2 (ER)]  Variant of MK/B61 
W82  LLNL  < 2 kT  XM785 155 mm Artillery Shell  Similar to W79 
B83  LLNL  1.2 MT 
B52 Stratofortress B1B Lancer B2A Spirit FB111A Aardvark 

W84  LLNL  200 T  150 kT  BGM109G Gryphon  Derived from MK/B61 Mod 3/4 
W85  LANL  5 kT  50 kT  MGM31C Pershing II  Derived from MK/B61 Mod 3/4; was recycled after retirement into B61 Mod 10 
[W86]  LANL  [MGM31C Pershing II]  Earthpenetrating warhead  
W87  LLNL  300 kT (W870) 475 kT (W871) 
LGM118A Peacekeeper (W870) [MGM134 Midgetman (W871)] 

W88  LANL  475 kT  UGM133A Trident II (Mk.5 RV)  
[W89]  LLNL  200 kT 
[RUM/UUM125A Sea Lance ASWSOW] [AGM131A SRAM II] 

[B90]  LANL  200 kT  NDSB (Nuclear Depth/Strike Bomb)  
[W91]  LANL  10 kT, 100 kT  [AGM131B SRAMT] 
In no particular order:
[1] Chuck Hansen: "Swords of Armageddon", 1995
[2] James N. Gibson: "Nuclear Weapons of the United States", Schiffer Publishing Ltd, 1996
[3] Stephen I. Schwartz (ed.): "Atomic Audit: The Costs and Consequences of U.S. Nuclear Weapons Since 1940",
Brookings Institution Press, 1998