Blue water navy means capability to exercise what is said as 'sea control'.
One should understand 'sea control' and 'sea denial'
Sea Control
Sea Control is the condition in which one has freedom of action to use the sea for one's own purposes in specified areas and for specified periods of time and, where necessary, to deny or limit its use to the enemy. There is likely to be a requirement for sea control across the spectrum of conflict. At the lower end of the spectrum, maritime forces may be used to ensure freedom of navigation by a deterrent presence in areas where illegal acts or constraints are being threatened or applied to merchant shipping. At the highest end it may be necessary to use a huge array of maritime power to eliminate an enemy's ability to challenge sea control over large areas of ocean. The need for sea control is not dependent upon the existence of a substantial threat. If there is any risk to freedom of action, sea control is necessary. If the risk is small, the capabilities that will be needed can be correspondingly modest.
Early achievement and retention of the necessary level of sea control will be a component of any major maritime operation or expeditionary campaign. However, there can be no absolute guarantee of protection from attack at sea unless command of the sea has been achieved. Sea control must be related to acceptable risk. For operations to take place, a working level of sea control must be achieved to provide sufficient freedom of action within an acceptable level of risk. If sea control remains in dispute in a certain area, each side will be forced to operate in the face of considerable risk.
However, sea control is most unlikely to be an end in itself; it is essentially a necessary condition to allow use of the sea for further purposes.
Sea Denial
Sea Denial is exercised when one party denies another the ability to control a maritime area without either wishing or being able to control that area himself. Classic means of achieving it are to lay a minefield or to deploy Sea Denial.
Sea Denial is exercised when one party denies another the ability to control a maritime area without either wishing or being able to control that area himself. Classic means of achieving it are to lay a minefield or to deploy submarines to threaten enemy surface forces; a more recent method, particularly appropriate in littoral operations, is to mount surface to surface missile batteries along the coast to pose an unacceptable level of risk to enemy surface units.
Sea denial and sea control operations are not mutually exclusive. The denial of the enemy's freedom of action is a consequence of effective sea control operations. Sea denial operations in one element or area of the maritime battlespace may be necessary to achieve sea control elsewhere.
However, the concept is only applicable when full sea control is not exercised by choice or out of necessity. At the operational and tactical levels, a zone of sea denial may be used as part of the outer defence of a force or area, or as a way of containing enemy forces.
At the strategic level, sea denial can be used in a guerre de course or sustained attack upon a nation's shipping to prevent reinforcement and to sap national morale and the ability to wage war.
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