Keeping Astute production moving between batches

The Astute example considers keeping batch-one boats in production while batch two was redesigned. An estimate mentioned in the discussion suggests that two additional boats could have fitted into the pause. Higher throughput might also have supported another batch-two boat. The resulting hypothetical force would contain five batch-one and four batch-two submarines. That nine-boat total illustrates the possible availability gains from continuing an established design until its successor is ready.