It was also supplied for delivery by UK-based Royal Air Force Valiant and Canberra aircraft[3] assigned to NATO under the command of SACEUR.

In addition, certain U.S. Navy carrier based attack aircraft such as the A3D (later A-3B) Skywarrior, A4D (later A-4) Skyhawk, and A3J (later A-5A) Vigilante were equipped to carry the B28.

[4] In February 1955 Sandia proposed that a basic warhead assembly be designed and that different noses, afterbodies, fins and fuzes could be attached to it.

Emphasis was placed on obtaining the optimum yield possible within the space and weight limitations assigned which necessitated having a much thinner case design than in previous weapons.

[7] It was decided that if the weapon could not be fitted to all of the required aircraft, first priority would be given to developing a bomb designed for subsonic internal or external carriage.

[6] Designers hoped though that they could produce a weapon considerably smaller than the 2,800 pounds (1,300 kg) and 25 inches (640 mm) diameter specified.

A timer was also considered having benefits in low-level delivery missions, but it was felt that these gains were slight and did not justify the complexity of the system.

The design used pyrotechnically actuated switches to control preheat current, timer selection, thermal battery arming, ground- and air-burst selection, contact fuze arming, timer motor starting, trajectory-arm-switch pressure-port sealing, gas boosting and even thermal battery monitoring.

At some point in the design the fuzing system was changed to allow for contact preclusion to be selected on the ground.

The external initiator system consisted of a power supply, precision timer and a neutron source called an S-unit.

During function the tritium ions were accelerated into the deuterium target which fused, releasing 14 megaelectronvolts (2.2 pJ) neutrons.

[15] The external configuration weapon had a length of 170 inches (4,300 mm) and weighed approximately 2,040 pounds (930 kg) with the nose section containing the fuze.

A low-altitude approach would help overcome this but would require a weapon that could survive impact with the ground before detonating once the aircraft was a safe distance away.

Sandia had been investigating the problem and believed that designing a bomb to survive an impact shock of 200 to 300 g (2,000 to 2,900 m/s2) was possible.

[20] The changes included a new altitude-sensing arming system to replace the baroswitches based on velocity sensing.

The bomb nose was given 8 inches (200 mm) of crushable honeycomb and another parachute was added, raising the total number to four.

The initial Mod 0 warhead lacked an environmental sensing device until concerns about accidental or deliberate (sabotage) detonation were raised.

[31][2] Four Mark 28 training variants (BDU-16/E) on their transporter (MHU-7/M) are on display in the Cold War Gallery at the National Museum of the United States Air Force in Dayton, Ohio.

The Mark 28 armed CF-104 Starfighters in Germany, 1963–72, under the "Dual Key" protocol (both the US and Canada had to agree to use, with the weapons in US custody on Canadian bases).