One of the first platforms specifically modified for this mission was the Martin P4M Mercator. Originally conceived and fielded in competition with the better known Lockheed P2V Neptune, the Mercator was bought in a relatively small quantity and subsequently modified to the electronic reconnaissance mission or ELINT, with the designation of P4M-1Q. Assigned to VQ-1 (Pacific) and VQ-2 (Atlantic) the Mercator was well regarded by the crews who flew it. Larger than the Neptune and powered by a hybrid power plant consisting of two Pratt & Whitney R4360 Wasp Major 28-cylinder radial engines, the P4M was 100 knts faster than its Lockheed rival when using the auxiliary jet engines. For take-off and other portions of the mission requiring extra boost, a pair of J-33 turbojets (De Havilland Goblin clones) was fitted in the rear of the two enlarged engine nacelles, the intakes being beneath and behind the radial engines. The jets, like those on most other piston/jet hybrids, burned gasoline, not jet fuel. With a fuselage built around a large bomb bay, the Mercator had ample room for a host of ELINT gear, supporting antennas and the crew to man it. Up front, pilots particularly enjoyed the view provided from the convex canopy and comfortable seating positions, essential for the 8+hour missions the ferrets flew. Heavy defensive armament was fitted, with two 20 mm cannon in an Emerson nose turret and a Martin tail turret, and two 0.5 in (12.7 mm) machine-guns in a Martin dorsal turret. Side window gun positions were [art of the original design but later discarded.
The ELINT mission was a necessary, but perilous mission. Sometimes it consisted of just drilling holes off the coast of countries of interest, collecting whatever signals may be in the air. Other times missions were flown in a manner to deliberately provoke a response in an attempt to collect against special air defense emitters. It was a necessary mission as in those days the nuclear strike capability of the US was limited to long-range bombers that would have to penetrate the thickets of air defense radars and fighters to deliver their weapons. Other aircraft flying the mission included PB4Ys, RB-29s and RB-50s, and RB-45s, as well as C-47s camouflaged as transports, all sufering losses as well. Later, more specialized aircraft would assume the mission with the appearance of the U-2, SR-71, RC-135 and EP-3.
Besides the Mercator lost off Shanghai and the other that successfully recovered in Japan, a third Mercator was lost over the Mediterranean when it crashed at sea with the loss of all hands after successfully evading Soviet MiGs over the Ukraine when it ran out of fuel. Entering service in 1950, by 1960, the Mercator had been replaced in VQ-1 and -2 with the EA-3B Skywarrior. There are no known examples left.
In Honor of those who served in the shadows and paid the ultimate price