In naval warfare, a "fleet in being" is a naval force that extends a controlling influence without ever leaving port. Were the fleet to leave port and face the enemy, it might lose in battle and no longer influence the enemy's actions, but while it remains safely in port, the enemy is forced to continually deploy forces to guard against it. A "fleet in being" can be part of a sea denial doctrine, but not one of sea control.

Admiral Arthur Herbert, 1st Earl of Torrington was an English Royal Navy officer, peer and politician. Dismissed by King James II of England in 1688 for refusing to vote to repeal the Test Act, which prevented Roman Catholics from holding public office, he brought the Invitation to William to William of Orange at The Hague, disguised as a simple sailor. As a reward he was made commander of William's invasion fleet which landed at Torbay in Devon on 5 November 1688, which initiated the Glorious Revolution.