Fast boats, submarines, and littoral sea denial

How serious are fast missile boats and conventional submarines as a threat to a larger fleet?

They can be potent littoral area-denial weapons, but aircraft, layered sensors, and ASW coordination make them much less decisive against a prepared blue-water force.

Fast small craft pose a greater threat close to shore, where geography and short distances favour them. A blue-water force can use airborne early warning, combat air patrols, and pickets to find and attack missile boats before they close the range. Conventional submarines can act as mobile minefields in an area-denial role, especially while they remain quiet in a chosen position. Moving consumes finite fuel or battery power and makes them noisier. A coordinated screen can combine active sonar from one platform with passive towed arrays and helicopter dipping sonar elsewhere, making the submarine's problem far harder.