Fleet in being

A fleet in being is a group of warships that is not strong enough to directly challenge its adversary, but can present a threat merely by its existence. This means that the enemy has to keep resources in the area to prevent the fleet from causing trouble.

A common example is the German fleet during both world wars. The German naval presence in northern Europe forced Britain to keep a fleet in the area, and its grip on the Mediterranean and other theaters was loosened.