Which would be perfect as, at first, JSS 1 and 2 could rotate into a mid-life refit. Then about 10-15 years later, JSS 5 and 6 get built. JSS 1 and 2 get retired (at about 25-30 years old), while JSS 3 and 4 go into mid-life refits in rotation.
And you finally achieve one of the original...