One of the main deficiencies with the otherwise superb F-4 Phantom was the lack of an internal cannon to supplement its air-to-air missiles and its air-to-ground ordnance. The Phantom was designed at a time when reliance on the missile was thought to have made a gun unnecessary. However, operational use in Vietnam had proved that there were still occasions when a gun was vital. Although the aircraft could carry an external gun pod this resulted in a loss of performance due to the extra weight and drag. A major redesign of the aircraft culminated in the production of the F-4E version. This model had a M61A1 Vulcan rotary cannon in an extended nose as well as other improvements over previous models. The F-4E was first delivered to the 33rd TFW at Eglin AFB in early 1968. The 40th TFS from Eglin supplied the first aircraft and crews which deployed to Korat on 17 November to re-equip the 469th TFS, replacing its F-105s. The 469th flew its first combat mission with the new aircraft on 26 November. The Korat-based 34th TFS re-equipped with the F-4E during May 1969 and the 366th TFW at Da Nang received two F-4E squadrons during the spring.