The yards needed for a sixty-eight-submarine force

How could Britain build twenty-four Vanguard-class and forty-four attack submarines?

It would need several new production lines - roughly three yards able to build four boats each - so that twelve submarines could be under construction at once.

The proposed force combines twenty-four ballistic-missile submarines with forty-four attack boats. At a four-year construction rhythm, a yard building only a few boats at once cannot create or replace that fleet before the oldest hulls age out. Production would need to sustain roughly eight to twelve boats simultaneously. That implies about three yards, each capable of working on four submarines at once, and makes industrial layout the core of the force plan.