The aircraft carrier is a large vessel which can carry up to 7 ship-bound attack fighters. The vast range of the aircraft means that they can be used for a variety of roles, from offensive operations to functioning as escort for your ships. Aircraft carriers are costly vessels and are vulnerable without other surface vessels to prevent submarine or battleship attacks, however, so you should be careful with them. Only major and minor powers are capable of building aircraft carriers, and Britain, Japan, France and USA have advantages regarding aircraft carriers. While some factions like Germany and Italy can choose to invest in an aircraft carrier, minor nations must capture a Naval Yard from a hostile nation to construct one.
This is the most common type of aircraft carrier, and is built by all major and minor powers.
The cheapest but the weakest of the lot, the Argus is the very first "aircraft carrier" on the block, and consists of a simple large ship. Although of British make, Argus does not have the British penchant for improved LOS, and is also available to the Japanese naval arsenal.
The Queen Elizabeth has a greater LOS, allowing it to spot for its planes before they've even launched into the sky.
The Yorktown has a cheaper ramp cost, making it easier for the American player to build plenty of these monsters to play.
The Bearn is not as strong as a normal aircraft carrier, but is cheaper than most and is tactically more sound than the Argus class.
The Joffre class serves as an upgrade to the Bearn, but isn't as strong as normal aircraft carriers are.