U.S. Army
Clark Field was the most important military airfield in the Philippines at the start of the Pacific war. It was established next to Fort Stotsenberg in 1919 as a small runway running along a highway just outside the base. By late 1941 it had a concrete runway capable of operating the heaviest bombers. Gasoline stores totalled 250,000 gallons and the field was protected by 12 3" fixed antiaircraft guns and 24 75mm truck-mounted guns. However, none of these could reach above 27,000 feet and their ammunition was incredibly unreliable; one estimate is that five out of six shells was a dud. The field based 19 B-17s of the 28th and 30th Heavy Bombardment Squadrons and 19 P-40s of the 20th Pursuit Squadron.
For reasons never adequately explained, the Japanese caught most of these aircraft on the ground eight hours after the attack on Pearl Harbor. Barely able to believe their good luck, the Japanese bombed and strafed the runway, destroying almost all the aircraft and ensuring control of the air over the Philippines.
References
The Pacific War Online Encyclopedia (c) 2007 by Kent G. Budge. Index