In May 1949, Martin submitted a proposal to BuAer for a two-seat, twin-engine, carrier-based jet attack airplane with the Martin rotary bomb bay.
My guess is that it was an attempt to take advantage of the A2D troubles at the time. Douglas got a letter of intent for the T40 turboprop-engine-powered A2D in June 1947. It was supposed to fly in March 1949. Because of T40 engine problems, it didn't fly until May 1950.
Thanks to the Glenn L. Martin Maryland Aviation Museum for the illustration.