First of all, there seems to be a lot of confusion and misinformation as to exactly how many carriers might have been docked at Pearl Harbor on December 7; the Japanese thought there might be as many as five. In fact, there were only two carriers, Enterprise and Lexington, near Hawaii at the time, and both of them were delivering aircraft to reinforce Midway and Wake. Enterprise had delivered planes to Wake and was scheduled to return to Pearl Harbor on Saturday, December 6, but bad weather delayed her and she was still some 2oo miles away on the morning of the 7th. The third Pacific Fleet carrier, Saratoga, was in San Diego picking up a new airgroup after having been dry docked at Mare Island for a minor refit. The other US fleet carriers, Ranger, Hornet, Wasp, and Yorktown were all in the Atlantic.

So the maximum number of carriers the Japanese might have damaged or sunk at Pearl Harbor is two. That would still leave five fleet carriers for operations in the Pacific once the Atlantic carriers had been transferred to the Pacific. As for the impact on the war, it would have been a blow to the USN, but probably wouldn't have immediately affected strategy or operations. I suspect, as some one else has pointed out, that the USN would rapidly salvage the damaged or sunken carriers and return them to service, probably in time for Coral Sea or Midway, at the latest.

Another point that seems not too well understood is the defense of Hawaii in relation to the "Europe First" policy. The US had three main priorities in it's war strategy, they were in order of importance, 1. The defense of North America (which was defined as the United States, Mexico, Canada, the Caribbean, and the "strategic triangle", i. e. a line drawn through Alaska, Hawaii, and the Panama Canal.) 2. The defeat of Nazi Germany, and 3. the total defeat of Japan. A careful reader will note that the defense of Hawaii carried a higher priority than the defeat of Nazi Germany ("Europe First"), therefore men, planes, ships, equipment, and supplies needed for the defense of Hawaii came before the buildup in Europe and even before war aid to Britain and the Soviet Union, and this held true throughout the war. Had the Pacific Fleet lost two carriers in the initial attack, there would have been no question of transferring the Atlantic carriers to the Pacific and reinforcing Hawaii's defenses with whatever was needed. Historically, Hawaii's air defenses were actually very quickly reinforced after the attack.

So what would have been the impact be on the war? Well, none to speak of. The USN would still have operated four or five carriers in the Pacific, and the two sunk or damaged at Pearl Harbor would have had the highest priority for salvage and repair, being returned to the fleet sometime in mid 1942. The light fleet carrier conversion program which enjoyed a high priority in 1942, would still deliver nine light fleet carriers in 1943. The Essex class carriers, under construction at the time, all enjoyed the highest priority in materials, labor and yard space, and most were delivered many months early, so that will not change. The lead ship, Essex, will still be commissioned on the last day of 1942.

The Japanese may be a little more complacent, but the first USN carrier raids will quickly change that and the Doolittle Raid will still lead to a battle of Midway which, in all probability, the USN will win. Guadalcanal will go forward pretty much on schedule and the Japanese will make the mistake of entering into a battle of attrition that will leave the IJN too weak to exploit it's advantage of interior lines when the US launches it's Central Pacific offensive in the latter half of 1943. I would think the major impact would be in the Atlantic where the Ranger will likely not be available for the North African Campaign in November, 1942, and the Wasp will not make deliveries of British aircraft to Malta; the British will have to use their own aircraft carriers for these tasks.