Submarines aren't really well suited for this. You want something that can search and monitor over a wide area, and then the ability to intercept and potentiall

Submarines aren't really well suited for this. You want something that can search and monitor over a wide area, and then the ability to intercept and potentially search/seize a suspicious vessel. The primary attribute of submarines is stealth, which is not relevant here. What you want is a combination of maritime patrol aircraft and offshore patrol craft. Maritime patrol aircraft (helicopter, fixed wing aircraft, UAVs) are equipped with surface search radar and other sensors that enable them to monitor a wide area. The patrol craft are also fitted with radars and sensors, and can also move to intercept a suspicious ship. A helicopter could also potentially be used for intercept