Submarines have the ability to deny the control of the sea to others without making use of it positively. Submarines cannot escort merchant ships, because they cannot defend against the other great danger, that of aircraft. Maritime patrol and attack aircraft are the last component of sea power to be considered. The ability to spot enemy ships first is an enormous tactical advantage. The Battle of Midway could not have been won without it.
Maritime aircraft are also significant carriers of ASMs in their own right.
The U.S. P-3 Orion, for instance, can carry up to 10 Harpoon ASMs. The Chinese have a number of different types capable of carrying one or two of their heavier missiles. For methodological reasons, aircraft-borne ASMs are much harder to count. Warships typically carry them in separate containers and do not carry reloads. A simple photo can suffice to show the total number of missiles that a ship can bring into combat.