W28 Nuclear Warhead
Weight: 1,500 - 1,725 lbs
Yield: 70 Kt - 1.45 Mt
Fuzing: Airburst or contact
Deployment Status: Manufactured 8/58 - 5/66, entered service (Hound Dog) 1959 and (Mace) 1960; Hound Dog retired 1/64 - 1976, Mace retired 1970; production - 900 (Hound Dog), 100 (Mace)
Comments: Warhead for the Hound Dog (AGM-28) and Mace (MGM-13) cruise missiles; 5 mods; PAL A and B
The Mk 28 was produced from 1958 through 1966. It used the W28 lightweight, Class D warhead (also shared with the TM-76 Mace surface-to-surface missile and the GAM-77 Hound Dog air-launched cruise missile). After 1968 it was redesignated B28.
Twenty different versions of the B28 were offered, distinguished by their yield and safety features. The B28 used the "building block" principle, allowing various combinations of components for different aircraft and roles. The B28 had a diameter of about 22 in (58 cm), with a length varying between 96 in (2.44 m) and 170 in (4.32 m) and weight of 1,700 lb (771 kg) to 2,320 lb (1,053 kg), depending on the model type and whether a parachute retard pack was fitted. The principal configurations were as follows:
B28EX — (EXternal), streamlined external-carriage version for free-fall delivery (no parachute)
B28RE — (Retarded External) streamlined external-carriage version with a parachute retarder (4 ft. pilot, 28 ft. ribbon chute)
B28IN — (INternal) unstreamlined internal-carriage version for free-fall delivery, primarily for the Republic F-105 Thunderchief
B28RI — (Retarded Internal) unstreamlined internal-carriage version with parachute retarder
B28FI — (full Fusing Internal) unstreamlined internal-carriage version with parachute for laydown delivery; used only by SAC B-47s and B-52s. The FI, for "Full Fuzing Internal" was developed to adapt to new low-level delivery techniques of the Air Force in the 1960s, and is the only model of this bomb equipped for air, ground, and delayed action burst.
The range of explosive yields was as follows:
Mod 1 — 1.1 megaton TNT equivalent
Mod 2 — 350 kiloton TNT equivalent
Mod 3 — 70 kiloton
Mod 5 — 1.45 megaton
The fuze mechanism on a B28 could be set for an air burst or ground burst detonation. A total of 4,500 B28s were produced. The last examples were retired in 1991.