Fleet in being

Arthur Herbert, 1st Earl of Torrington, originator of the term "fleet in being" in 1690

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.