The F-15N Sea Eagle was proposed as the carrier capable naval variant of its F-15 Eagle by McDonnell Douglas when the USN started looking for substitutes for its F-14 Tomcats, which, despite of being highly capable, were really expensive to maintain. In fact, the high acquisition as well as operating and sustainment costs of the Tomcats; with a single F-14's acquisition cost almost equal to 3 F-35s in dollar purchasing power terms; made the program reach the very top of the Congress' chopping list for defense programs. The F-15N was to have strengthened landing gear & folding wingtips for carrier based operations besides variable sweep wing. However, cost evaluation of the proposal along with inability of the Eagle to carry the long range Air-to-Air AIM-54 Phoenix missiles (considered as the go to aerial weapon of the time) collectively & effectively terminated the F-15N Sea Eagle at the proposal stage itself and ensured an extended life span for the F-14 Tomcats.

Audio Credits: Alex Hollings of SandBoxx News on F-15N