A Successful Runner-Up
The Glenn L. Martin Company's P4M Mercator ranked behind the Lockheed P2V Neptune as a maritime patrol aircraft.1 Still, the Mercator had a successful, decade-long career as a U.S. Navy spyplane.
In 1944 the Navy initiated a number of new aircraft programs, several with turbine (jet) engines. Two prototypes of the advanced XP4M-1 maritime patrol aircraft-powered by both piston and jet engines-were ordered in July 1944. The contract went to the Martin firm less than three months after the Navy ordered two XP2V-1 Neptune prototypes and 15 production aircraft from Lockheed's Vega division.
While rated as a patrol aircraft, the Mercator's official documentation noted: "The P4M-1 is a mine laying and attack aircraft. Secondary mission is long range patrol and search."2