Just like the strategic air war navies spend most of their time on missions in strategic areas, but are also able to move province by province. When in a strategic area each fleet has a value indicating how spread out it is. In general a more spread out fleet can cover more area and have a higher chance of finding the enemy, but will take time to concentrate its forces and bring them all to bear. Things like how fast fleets of a certain composition can converge and how well they can search in an area is controlled in large part from Naval Doctrines. We'll cover those in detail in a future diary, but as an example if you pick the Trade Interdiction doctrine you can unlock Wolfpack tactics which will make sure your subs find more targets and can all get together and strike more often.