Martin Model 219

P4M-1 Mercator Patrol Plane
Variants/Specifications

Nineteen forty-four was a fertile year for Martin's engineers. With earlier projects like the B-26 and Baltimore winding down, and the unwanted B-35 shifted back to Northrop, they had time and energy to launch no fewer than six new designs: the XB-48, AM-1 Mauler, 2-O-2 airliner, XPBM-5A amphibian, JRM Mars, and Model 219 P4M-1 patrol plane for the Navy, dubbed the "Mercator." The Mercator shared several features with its Martin contemporaries. Like the Mars and Mauler it was powered by the Pratt and Whitney R-4360 "corncob" engine, which was becoming a Martin specialty. So was the high tail fin also seen in the 2-O-2 and XB-48. Like the XB-48, the Mercator had jet engines, two Allison J33's mounted beneath the big radials in the same nacelles.

The intended mission was long-range maritime patrol. Experience in World War II had shown the Navy that this need not be limited to flying boats: faster landplanes like the Lockheed PV-1 Ventura, PV-2 Harpoon, and Consolidated PB4Y Liberator and Privateer had been useful as well. In 1944, the old "Patrol" category was revived and applied to purpose-built landplanes that would combine the size and armament of four-engine planes with the economy and range of two-engine ones. Besides two XP4M-1 Mercators, the Navy ordered another prototype, the XP2V-1 Neptune from Lockheed.

As had been the case with the Mauler and Skyraider, Martin's competitor offered an older, less complicated plane. Like the Skyraider, the Neptune used Wright R-3350 engines. Lockheed had begun work on its design work as far back as 1941, and the Neptune was already a year into flight testing before the Mercator first took off in September 1946. The same month, a modified P2V called the "Truculent Turtle" covered a record 11,236 miles nonstop.

The Mercator offered several advantages, however. A third larger than the Neptune, it was also 100 mph faster when the jets were used. Combining two different types of powerplant in the same plane, however, proved difficult. Both piston and jet engines were adjusted to burn a highly volatile common fuel; when an XP4M-1's main fuel line burst on a test flight in August 1947, fumes killed a Martin flight test engineer and injured two others.

The Navy chose the cheaper, more reliable Neptune as its regular patrol plane; it was to continue in service even longer than the Skyraider. But the Mercator was not a completely lost opportunity for Martin - nineteen were ordered in 1947 and 1948. Most were delivered to Patrol Squadron 21, stationed at Patuxent River Naval Air Station in Maryland and later Port Lyautey in Morocco. Fast and heavily armed with nose and tail turrets with 20mm cannons and a 250CE Martin deck turret with twin .50's, Mercators were better suited to bombing and mine-laying missions in hostile airspace than to antisubmarine patrol. Beginning in 1951, they were specifically modified for electronic reconnaissance as P4M-1Q's. Serving with a variety of small, secret units, their tail numbers sometimes disguised, Mercators were sent out to monitor radar and radio signals along the coasts of the Soviet Union and its allies. Long patrol missions were conducted at night, the planes loaded with electronic black boxes and crewed by 14 pilots, operators, and gunners. Occasionally they met with opposition. There were rumors of a hostile attack after a Moroccan-based Mercator crashed in the eastern Mediterranean in February 1952. Another Mercator was definitely shot down by Chinese fighters near Shanghai in 1956. Still another fought off attacks by two North Korean MiG-17's in 1959, the tail gunner being wounded in action. Mercators conducted their own secret Cold War until being retired in 1960. None survives today.