The U.S. Navy and Marine Corps are growing more concerned at the increasing age of their warplanes. Fighters and bombers average twelve years, helicopters are nearly twenty years old, on average. At current procurement rates, it will take 26 years to replace the entire inventory. While older aircraft can be maintained in combat worthy condition for decades, it costs more the older the aircraft get. The navy is currently buying new F-18s to replace F-14s, and will be buying a 480 F-35s, but these won't begin showing up until 2008.