How could Britain add submarine force multipliers around its SSNs and ballistic-missile boats?
Short answerIt could add cheaper SSKs, or build two extra Dreadnought-family hulls configured as SSGNs with the potential to backfill the ballistic-missile role when required.
NotesThe surface-ship numbers argument also applies to Britain's submarine force. One option is a group of diesel-electric SSKs that multiply the reach of expensive SSNs and provide cheaper training and regional patrol capacity. Another is two additional Dreadnought-family boats fitted with removable launch-tube inserts for cruise or future hypersonic missiles, creating an SSGN force that could also cover ballistic-missile availability in an emergency. Both options add resilience and force multiplication, though changing a boat's strategic role would be more involved than simply swapping inserts.