The Age of the Aircraft Carrier

World War I was marked by the dominance of the battleship. These heavily armed behemoths of the sea were the highest class of ships at the time. This all came to change with the advent of the aircraft carrier. Although successful air raids had been launched from ships before, the first war where the carrier had its chance to truly shine was World War II. The aircraft carrier could be loaded with a plethora of airplanes, making air superiority easier to achieve, as carriers functioned as mobile bases. The carrier's versatility made it shine over the battleship. Not only more effective in land assaults (airplanes can cover more area than cannons), airplanes could also be deployed to take down battleships, as the anti-air guns on these were not incredibly effective.
As the Navy has been in constant decline ever since World War II, little innovations have arisen, meaning carriers are still the top of the line. Carriers are, however, incredibly expensive by nature. Not only do they require massive amounts of resources to build one (just imagine the steel needed...) but you also need to, well, as the name implies, load it with airplanes. Planes...tend to be on the expensive side..for example, a single AV-8B Harrier II costs anywhere from 24 to 30 million dollars. The larger carries can be equipped with up to 85 planes. In short, aircraft carriers are risky investments, as if one sinks, the losses incurred are tremendous.
Aircraft carriers are predominantly used by the United States, who has 10 Nimitz Class (the big ones) and 9 smaller ones. The United Kingdom, by contrast, has 1. Carriers are only used nowadays to maintain a strong global presence, with the ability to quickly deploy planes anywhere.