Seapower has for millennia been measured in disparate ways, from protecting or attacking trade routes, to guarding the coast against incursions or projecting friendly armies onto far shores. In every era the ability to do each of these came to rest on the combat power of a particular type of ship, the navy possessing the larger number having the power to utilize the seas for its desired purposes.
Ancient navies counted oar-powered galleys, the vessels progressing over the centuries from the penteconter through biremes and triremes to quinqueremes, each generation possessing more oars and/or more rowers per oar. Combat was a combination of ramming to sink an opposing ship, or boarding to capture one.
Aircraft Carriers: Every age of naval warfare is dominated by one ship type, from ancient galleys through ships-of-the-line to dreadnought battleships. The middle of the 20th century was dominated by the aircraft carrier, and they remain a fixture in major navies to this day. The aircraft of the day were only good for observation, but in that role they gave a fleet eyes beyond the horizon for the first time in history. As aircraft became more powerful, the carrier challenged, then supplanted, the battleship as queen of the sea. Today carriers are in turn being challenged by long range missiles, nuclear attack submarines, and space-based platforms.