The decisive factor for the US victory at the Battle of the Philippine Sea, was their plan to defend the carriers from the Japanese raids and destroy them, before launching their own counterattacks on the enemy carriers. This would allow the American fighters to focus on destroying the Japanese raids exclusively, rather than splitting the air forces by sending out strike missions with fighter escorts, to hit the enemy carriers at the same time.

In 1942 this would have been disastrous for the US, and the Japanese planners were counting on this, but in 1944 improvements in US crew training, equipment and radar directed fighter interception gave them the advantage. These improvements had been a signifiant undertaking. This plan was a huge risk for the US, as they would be exposing their carriers to continuous Japanese raids , without hitting back at them at same time, like at Midway. Radar gave about 30 minutes warning from when the Japanese raids left their carriers, allowing for the US fighter to get to altitude. Intercepts were made by the fighters 60 miles out from the carriers. The Japanese did drop some 'window' chaff to confuse the radar, but the effect of this was negligible. The Japanese aircrews were inexperienced after losses encountered in prior battles, and the Americans knew this. Heavy losses were encountered in this battle by the Japanese as their fighters did not always stay with the bombers during the raids. This allowed the forces to be separated by the US combat air patrols and destroyed. Inexperienced enemy bomber and torpedo crews missed valuable opportunities. The US had also upgraded their AA defence systems, and had developed new doctrine for its use. Ships formed circular defence-in-depth cordons around the carriers. As enemy planes made it through the CAP they were subject to waves of AA fire coming up from the cordon as well as off the carriers themselves. The cordon began with 5in guns, then the next ring would be 40mm, then 20mm. The US carriers kept their decks clear, so individual planes could land to rearm, refuel then return to the fight. Radar allowed the US fighters to intercept Japanese land based fighters as they came in to land on Guam. After the three main Japanese waves had been repulsed, the US was able to go after the Japanese carriers, losing 20 aeroplanes, and destroying three carriers. The US forces then had to land on their carriers at night, which cost a further 80 aircraft.

Despite winning the largest carrier battle of all time, Admiral Spruance was still disappointed, as they had not destroyed all of the Japanese carriers. Spruance had positioned the fleet prior to the battle based on the assumption that the Japanese would split their forces to go after both the US invasion fleet and their carriers. This was not the case, and the remaining Japanese carriers were able to break off and escape to Okinawa. For the Japanese the decisive battle had been lost, with only 35 aircraft remaining from a carrier force of 430. In the end, the battle came down to the superiority of the US aviators and aircraft, and the effective use of Radar assisted airborne interception.

Source: The Philippine Sea 1944. By Mark Stille.