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In a war in which two of the major combatants, America and Japan, were 5,000 miles apart, with Great Britain a further 10,000 miles away, it was inevitable that a substantial part of the Pacific War would be fought on water. Added to this was the fact that Australia, another major combatant in the war and the base of US Army Operations under General MacArthur, was 3,000 miles from Japan.

For the entire period up to Pearl Harbor in December 1941 it was assumed that the battleship would be the key weapon that would determine the outcome of this conflict. In a single morning, events at Pearl Harbor overturned this perception. From now on it was clear that the aircraft carrier and their aircraft would dominate the fight for the vast stretches of the Pacific Ocean and the thousands of islands that populated it.

It is interesting therefore to look in detail at the carrier fleets of the combatants. As the attached aircraft carrier chart [See US Fleet Carrier Chart] shows Japan started the war with twelve fleet carriers of which half were light fleet carriers. Set against them the United States had six fleet carriers. Although two of these were lost at the Battle of the Coral Sea and the Battle of Midway, Japan’s numeric advantage was considerably reduced with the loss of 4 of their 6 frontline aircraft carriers. Nevertheless in the aftermath of Midway Japan remained a formidable Naval competitor. During the six month long Guadalcanal campaign, the Japanese Navy demonstrated superiority in traditional surface battles, showing particularly strength in torpedo technology and night fighting. Furthermore in the second of the two major carrier-on-carrier battles of the Guadalcanal campaign, the Battle of the Santa Cruz Islands, the Imperial Japanese Navy scored a clear tactical victory. At this point in October 1942 the United States had just two aircraft carriers in the Pacific compared to Japan’s eight.

However Japan was unable to press its numerical advantage in carriers because in the first twelve months of the war it had lost two entire batches of trained aircraft carrier pilots. Because Japan had always anticipated a short war decided by a decisive battle, such as the naval victory at the Battle of Tsushima in Russo-Japanese War [1904-5], it had made inadequate investment in the pilot training capacity needed for a prolonged conflict. The result was that the Japan Navy was forced to retreat either to Japan’s Inland Sea or to Singapore and Borneo. MacArthur’s rampaging advance up the east and northern coasts of New Guinea in the 18 months after Japan’s retreat from Guadalcanal went uncontested, as did Admiral Nimitz’s advance through the Gilbert Islands and Marshall Islands in the Central Pacific.

During this period Japan’s carrier force in the Pacific increased from 8 carriers to 11 carriers while the US fleet went from 4 carriers to 19 carriers. The product of America’s pre-war rearmament had finally arrived. In addition to 8 new Essex Class fleet carriers, as a result of Roosevelt’s personal intervention in January 1942, cruiser hulls had been converted into 9 Independence Class light fleet carriers. The change in numbers of aircraft carriers available to both sides was dramatic. Nevertheless with 11 carriers in the Japanese fleet, the Imperial Japanese Navy still felt itself to be competitive because it could command a land based air force on Saipan and adjacent islands (‘unsinkable aircraft carriers’) of 300 aircraft. For the Imperial Japanese Navy it was now or never for a decisive battle before America’s production of new aircraft carriers became overwhelming.

In the event the Battle of the Philippines Sea (the Great Marianas Turkey Shoot) turned out to be a catastrophic defeat for Japan. The cause of this defeat was much less about numbers and much more about quality. In the 18 months after Guadalcanal the United States had not only produced a brand new navy, it had produced a navy that was vastly more technologically sophisticated than the navy that had started the Pacific War. The USS Essex with 33 knot top speed and its three lifts, one of them fitted to the side of the ship, making it much more bomb resistant, was the best aircraft carrier of the Pacific War.

More importantly the new breed of ship based aircraft, notably the Grumman Hellcat and the Vought Corsair fighters, were vastly better than the Grumman Wildcat fighter that started the war. In addition improvements to aircraft to ship communication and radar led to a massive improvement in the command and control functions of the US Navy. Advances in computer controlled anti-aircraft guns had also vastly upgraded the defensive capabilities of the US surface fleet whose main task now was to protect its carriers. These were advantages denied to the defense of Japan’s carriers. Lastly it should be noted that two of Japan’s carriers at the Battle of the Philippines Sea, Shokaku and Taiho, were sunk by US submarines. By mid-1944 the problematic Mark XIV torpedoes had finally been made to work and operation control of US submarines had significantly improved; an ability that was significantly advanced by the Allies by now vast resources in code-breaking intelligence gathering and analysis.

After the Battle of the Philippine Sea, although the Imperial Japanese Navy still had 9 carriers compared to the United States’s 19, most of these carriers were aged, worn out, and technologically outdated. Even more importantly a third generation of navy pilots had been obliterated. These pilots, themselves pale shadows of the brilliant navy fliers who had started the war, proved to be irreplaceable. Lacking instructors, planes, aviation gasoline, the Imperial Japanese Navy was never able to replace its Navy pilots. As a result its carrier force at the Battle of Leyte Gulf, instead of being the cutting edge of its navy, had to be used as bate to draw Admiral Halsey away from the St. Bernadino Strait dividing the main Philippine island of Luzon from Samar Island. Although the tactical deception worked, the battle was still a crushing defeat for Japan. In this last throw of the dice the Imperial Japanese Navy lost four more carriers, 3 battleships, 10 cruisers and 11 destroyers and what remained of its aircrews. As a coherent force the Japanese Navy had ceased to exist.

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