Why fleet modernization works best as a rolling program

Was the Royal Navy's 1920s modernization only one stage of a gradual replacement program?

Yes; staged modernization was economically and technologically preferable to rebuilding the whole fleet at once.

Modernizing an entire fleet at once creates a damaging boom-and-bust cycle for shipyards and crowds out merchant orders. A continuing program spreads expenditure and labor demand, allows later ships to receive newer technology, and lets each refit teach lessons for the next one. Naval readiness depends partly on the health of the industrial base that supports it.