How fleet size affects maintenance and availability

The one-in-three availability rule becomes more favourable as the pool of ships grows. In the examples given here, four ships usually provide two available hulls, while five make two more consistently available. A twelve-ship force can support about six operational ships, with a larger number available more broadly. Spare capacity allows repairs and maintenance to proceed at planned times, which makes those periods easier to organise and shorten. Repeatedly postponing work because too few ships are available eventually leaves ships unable to operate until maintenance is completed. The Royal Navy's Type 45 destroyers and submarines illustrate that problem.