Convertible submarine tubes and a five-hull deterrent reserve

Four boats are normally associated with guaranteeing continuous at-sea deterrence. This proposal builds five compatible Dreadnought-type hulls while publicly assigning only three to the ballistic-missile role. Inserts in the other two boats' large missile tubes would let them carry conventionally armed cruise missiles as SSGNs, providing a day-one strike option when conflict was expected in advance. If collision, refit delay, or another accident removed an SSBN from service, one SSGN could return to the deterrent role. The common class combines a declared reduction in ballistic-missile boats with physical redundancy.