Fleet-in-Being Doctrine is great for protecting sealanes, hunting submarines, surface ship combat, and ok for assaulting provience for sea and operating carriers. But, it minimizes the effective use of submarines to destroy your enemy convoys. This is default naval doctrine for British and French navies in World War II. It is a great sea doctrine maintain a oversea operations and keep supplies flowing your forces oversea. It maximize your organization but modest improve in morale of your naval units. The effects are increase of 20% in organization and 10% in morale of naval units.