Development of the D5 Submarine Loaded Ballistic Missile (SLBM) followed the president’s call to modernize strategic forces in 1981. The original plan for the D5 was to equip the force solely with a new higher-yield re-entry body, the Mk 5. The predecessor SLBM, the C4, was equipped with a smaller and lighter, lower-yield re-entry body, the Mk 4. During initial development, SPA assessed configuration options for the SLBM D5 concept, which later became the Trident II missile.
The configuration options SPA examined included using a force equipped with only Mk 5 re-entry bodies as well as mixes of missiles carrying either Mk 4 or Mk 5 weapons. The prior evolution of SLBMs from Polaris (A1) to Trident I (C4) included a larger number of warheads or a new larger-yield warhead for each new missile. The idea to engineer the D5 with the option to carry either of two different re-entry bodies was unprecedented at the time. The approach would require additional development to allow missile fire control and flight systems to accommodate either warhead. Opposition to the expense associated with this effort was considerable.
SPA’s analysis that supported development of the D5 to carry either the Mk 4 or Mk 5 warhead resulted in a flexible and effective mix of weapons across the target spectrum.
SPA assessed various deployment options for the SLBM force, including missile range, accuracy, and yield; threat target bases; submarine at sea deployment options; potential threat Anti-Submarine Warfare capability; and potential anti-ballistic missile defenses.
When environmental concerns threatened to shut down the production facility, SPA’s analysis enabled the force to respond to a shortfall in Mk 5 re-entry bodies without retroactive reconfiguration of the missile.
SPA’s modeling illustrated the increase in force capability across the potential target spectrum that would result from deploying D5 with both Mk 4 and Mk 5 re-entry bodies. As a result, national defense leadership decided to develop this augmented capability for the D5 missile.