Lockheed's F-35 fighter jet is more popular than ever, but falling prices may be taking a toll on profits.Valued at almost $120 billion, with nearly$72 billion in annual revenue yielding $4.2 billion in annual profit, Lockheed Martin (LMT -0.53%) remains the most valuable pure-play defense stock in the world. (Although if you look at market capitalization exclusively, one could argue Palantir (PLTR -5.39%) is even bigger, despite boasting much smaller revenues.)Best known for its military aircraft, in 2024 ...