A few years ago, Chairman of the Joint Chiefs of Staff Admiral Mike Mullen assured Lockheed Martin (NYSE:LMT) investors that their company's F-35 Lightning II fighter jet was the only game in town -- probably the "last manned fighter jet" the U.S. would ever build. Fast-forward a few years, and the Pentagon's under new management. Air Combat Command Mike Hostage now says that the U.S. needs a whole "family of systems" for its Air Force, and could begin building a new, sixth-generation fighter jet in as little as 18 years.

What does this mean for Lockheed and for the F-35's engine builder, United Technologies (NYSE:RTX)? What opportunities does it open up for rival plane builders such as Boeing (NYSE:BA) and Northrop Grumman (NYSE:NOC)? Listen in, as Fool contributor Rich Smith explains.