But what made the F-111 great? Did the United States truly lose any capability by retiring it? Here's What You Need to Remember: The F-111 first was tested in combat in Vietnam during 1968, but issues with the design delayed its full fielding until Operation Linebacker. It would go on to become one of the most survivable bombers of the war due to its ability to penetrate at a low level, with only a 0.015 loss rate. The F-111 Aardvark was the U.S. Air Force’s premier strike aircraft for the majority of the Cold War. It served in practically every conflict from Vietnam forwards, until it was replaced by the F-15E Strike Eagle. It also served Strategic Air Command in a limited role as a strategic bomber.