The F4U-4 is the last variant to see action during World War II, deliveries to the U.S. Navy of the F4U-4 began late in 1944. It fully equipped naval squadrons four months before the end of hostilities. It had the 2,100 hp engine. When the cylinders were injected with the water/alcohol mixture, power was boosted to 2,450 hp (1,830 kW). The propeller was changed to a four blade type. Maximum speed was increased to 448 miles per hour (721 km/h) and climb rate to over 1,180 m/min as opposed to the 884 m/min of the F4U-1A. The service ceiling also increased significantly from 11,000m to 12,000m.