Sea denial is a military term describing attempts to deny the enemy's ability to use the sea without necessarily attempting to control the sea for its own use. It is a less ambitious strategy than sea control and can potentially be carried out by asymmetrical warfare or by maintaining a fleet in being that threatens offensive operations without actually conducting them.
During World War I and World War II, Germany pursued sea denial using U-boats. Owing to the substantial superiority of the Royal Navy's surface forces Germany's Imperial Navy (in World War I) and Kriegsmarine (in World War II) had little hope of seizing control of the high seas, but with submarines the Germans could hope to defeat the British by choking off their crucial access to seaborne commerce. In both wars, the United Kingdom successfully resisted the German strategy with a combination of strict rationing and the development of anti-submarine weapons and techniques. During the Cold War, the Soviet Union invested heavily in submarines and would likely have pursued a similar strategy of sea denial had tensions with the NATO powers escalated to open warfare.
Since World War II, the most historically notable instance of a sea denial strategy being attempted involved the so-called 'Tanker War,' wherein Iran and Iraq sought to close the Persian Gulf.
Modern sea denial relates to the area denial weapon, for example in the context of a land power using land-based missiles to strike sea targets. Such missiles can follow cruise missile (terrain-skimming) or ballistic missile trajectories. In response to these threats, the U.S. Navy has developed the Littoral Combat Ship.