did not deploy and prevent bomb-arming. The Mk-28RE (retarded external) was long and weighed . The design consisted of the Mk-28 Mod 1 Fuze and a set of Mk-28 Mod 0 RESC (Retarded External Shape Components). It was only available with the Mod 1 warhead. The Mod 1 warhead had the same yield options as the Mod 0, but not all yield options were stockpiled. The Mk-28RI (Retarded Internal) weapon was designed released in April 1959 and achieved production in June 1960. The design weighed and was long. The design consisted of the Mk-28 Mod 2 Fuze and the same Mk-28 Mod 0 RESC as the RE weapon. It also used the Mod 1 warhead. FI weapon The Mk-28FI was the true laydown weapon desired during the development of the RE and RI weapons. The weapon was based on promising results from the TX-28-X2 warhead (which became the Mod 1 warhead) and would have a full-fuzing option capability. Previous weapons required a B-52 bomber to fly at at least for the weapon to survive laydown. It was hoped that a true laydown weapon would reduce this height to under . The proposal included requirements for delayed ground burst (laydown), retarded air burst, free-fall air burst and free-fall contact burst fuzing. The selection of air or contact burst would be selected via aircraft control equipment while the laydown option would automatically engage if the weapon was dropped below a certain pressure altitude. Most components were sourced from other programs meaning the main task of the program was developing a shock-mitigating structure and conducting fuze tests. In August 1960 operational requirements for the TX-28-X3 warhead were issued. These requirements included the capability to survive release from and to be carried internally by the B-47 and B-52 bombers. The bomb nose was given of crushable honeycomb and another parachute was added, raising the total number to four. The Mk-28FI weapon was design released in October 1961. The weapon was in diameter, long and weighed . The design consisted of a Mk-28 Mod 3 fuze and Mk-28 Mod 0 FISC (Full-Fuzing Internal Shape Components). The weapon could not use previous Mk-28 warheads, only being suitable for the TX-28-X3 (now called the Mod 2) and later warheads. The laydown and retarded airburst time for the weapon was 79 seconds. In laydown mode, the weapon had to be dropped between to allow the weapon to reach