EL CENTRO, CA - NOVEMBER 3: A cloud of dust envelops a helicopter as members of the UK's Royal Air Force (RAF) practice low-visibility Ôdust landingÕ while flying over parts of Imperial County and in Anza-Borrego Desert State Park during Merlin Helicopter training out of Naval Air Facility (NAF) El Centro in Exercise MERLIN VORTEX on November 3, 2009 near El Centro, California. The RAF chose the southern California desert in part for its variety of hot and often dusty desert and rugged high mountains for training pilots and acclimatizing troops and Merlin helicopters for the extreme environments they will face upon deployed to Afghanistan later this year. The exercise to prepare 5 flights of 29 (Army Co-operation) and 78 Squadrons began in late August and will conclude in late November. (Photo by David McNew/Getty Images)