Sea Lanes Denial is a tactic aimed at disturbing or destroying enemy naval activity in a defined area and provide a reasonable protection to friendly naval operations in the same area.
It can be part of a greater Naval Superiority strategy.
To understand how it works, imagine a "corridor" in the sea: own naval units will use this "corridor" to reach their target and perform any required task. The "walls" of this corridor are made from fixed or mobile threats against enemy air or naval activity, anything that can deliver damage to friendly naval units.
So, for example, two distinct groups of Submarines (anti-naval and anti-submarine weapons), Frigates (early warning) and Cruisers (Anti-Air, long range early warning) will patrol the two 'sides' of the corridor, one each. If the corridor needs to be very long, it's better to use several lighter, shorter ranged patrols than one strong and longer ranged. This will keep the whole length under constant screening.
This tactic can also be used to cut off enemy fleets: by deploying the "walls" on the sides of A likely avenue of approach it can effectively funnel enemy units onto friendly positions and make their destruction much easier.
It can be very useful to keep a rapid-response reserve of Torpedo Bombers ready to deliver added firepower quickly when needed.
Cybran Harms Torpedo Defense do wonders against enemy ships too.