The advent of the carrier, in U.S. Navy service, began with the light carrier and former collier Langley, which entered service with the Navy in the 1920's. She was the predecessor of a far more versatile and capable class of carrier, the Lexingtons. 

    Using the hulls of the Constellation-class battlecruisers, which had to be scraped due to the limitations of the Washington treaty of 1922, Lexington and Saratoga became the largest carriers in the world, and were not succeeded in this rank until Japan fielded the Shinano. 

    Following the Lexington class, which received the hull numbers CV-2 and CV-3, was the Ranger. This single ship will not be discussed here, as it did not deploy for active warfare into the Pacific. 

    However, following the Ranger was the probably most succesful pre-war design of carrier, the Yorktown-class. This class of carrier was originally only consisting of Yorktown and Enterprise. This was due to the limitations imposed on the nations which had signed the Washington treaty. Carrier tonnage for the United States and Britian was limited to 135.000 tons. With the 72.000 tons of Lexington and Saratoga, plus the 14.200 of Ranger, plus the 19.000 tons for each Enterprise and Yorktown, the total US carrier tonnage had reached 120.000 tons, and thus, there was not enough tonnage left to build a third carrier of the Yorktown-class. The gap still existing, 15.000 tons, was still large enough to build a carrier "into it". The result of this was the carrier Wasp, weighing 14.200 tons standard.   

    The end of the treaty limitations however gave the US the chance to greatly improve the striking power of it's carrier fleet. The first ship build was a slightly improved version of the Yorktown, the Hornet, being commisioned into the fleet four years after her sisters.   

    In the course of a general modernization and extension program for the fleet, in 1940, a program was announced to build 32(!) Essex-class carriers. The Essex' were the most advanced carrier class the US fielded in World War 2. Ships of this class would serve the fleet until well into the 1970's, and some of them were kept in reserve for as long as 1989.   
The last class of carrier that can be called "fleet carrier" was the Independence-class, actually an emergency program to build more carriers more quickly. Taking the hulls of uncompleted Cleveland-class cruisers, the Independences were an important aid to the Allied war effort. Their duties mainly included fighter protection for the fleet and sometimes aircraft ferrying.   

    During the war, the carriers proved what had become clear to far-sighted naval officers (meaning in this context, aviators) ever since the Lexingtons had so successfully conducted wargames in the 1930's. With the attack on Pearl Harbor, and the de facto destruction of the US battlefleet, the carriers and their cruiser escorts became the principal fighting weapon. 

    The Japanese Combined Fleet ruled the seas for six months, until, at Midway, it lost four of its nine remaining carriers.  Two more carrier engagements fought in 1942, Eastern Solomons and Santa Cruz, showed that the Japanese had not yet thrown in the towel; but their performance deteriorated rapidly. However, through the whole year of 1943, neither side was wanting another carrier battle. In 1943, the big time of island-hopping began, and the Solomons were being secured, creating many small surface engagements in the Solomons. 

    As the year 1944 began, however, the US Navy was moving toward more important targets, targets the Japanese could hardly afford to loose. Thus, the very last carrier battle of the war (not counting Cape Engaño, which was everything but a "battle"), the Battle of the Philippine Sea, showed how useless the former sharp-edged sword of the Imperial Navy had become. It showed that carrier fleets required a far greater logistical support than battlefleets; because carriers had to constantly receive able pilots, while battleships were usually not short on able gunners.   

    The Japanese had failed to produce replacement pilots, and paid. The Marianas Turkey Shoot destroyed the Japanese carrier air groups.   

    A final battle would be fought by the US carriers against the IJN, at Leyte. By this time, Japanese carriers were reduced to the role of decoys, and the main targets the US Navy should have attacked were battleships and cruisers. The result was showing the immense power of US carrier air forces. Without the ability to fight back in a useful way, the IJN suffered horrendous losses for little or no gain.   

    The Battle of Leyte Gulf marked the end of organized naval resistance, and afterwards, US carriers conducted what would today be called "power projection", attacking land-based air units of the Japanese, striking targets deep in enemy territory. So powerful was US air defense becoming, both on the carriers and their escorts and in the air, that the Japanese send their rookie pilots in deliberate suicide attacks, crashing into the ships along with their planes.   
This proved an deadly, though desperate way to fight back. At Okinawa, the Japanese hit 11 carriers (counting also pre-invasion hits), but managed to sink none. However, the smaller ships suffered extremely heavy casualties (see Destroyers, Auxilliaries).   

    Until the end of the war, the US carriers succeeded in sinking most of the rest of the Japanese fleet, and destroyed most of the Japanese air forces.   

    What should be noted when discussing the subject of the Pacific War is, although the war's best known and most spectacular  battles were fought by carriers, is that of the 36 most important battles, only five were purely carrier engagements which can be called battles (discarding in this context the Battle of Cape Engaño, which was by no means a fair fight). Four of these were fought in 1942, when offensive carrier strike power was overwhelming for the defensive tactics. Carrier tactics was, thus, he who struck first won. Of these, the battle of Midway was the most devestating carrier battle, with five carriers out of seven that actively participated in the battle sunk. A clear sign of the offensive/defensive ratio of carriers in 1942 is the fact that USS Enterprise was solely responsible for the destruction of Akagi, Kaga and Hiryu,while USS Yorktown of the same class was unable to defend itself against a single carrier's strike power, Hiryu's.   
Carrier battles were, in 1942, thus like the battlecruiser matches of the earlier war: both sides carried the weapons to defeat the other side many times over, but neither was even close to well protected. 

Fleet Aircraft Carriers 
CV-1 Langley
CV-2 Lexington class
CV-4 Ranger
CV-5 Yorktown class
CV-7 Wasp
CV-9 Essex class
CVL-22 Independence class
Escort Aircraft Carriers
CVE-1 Long Island
CVE-9 Bogue class
CVE-26 Sangamon class
CVE-55 Casablanca class
CVE-105 Commencement Bay class