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
The Mercator was an extremely attractive, streamlined aircraft with a shoulder-position wing, a design that provided both high-lift and high-speed characteristics for a patrol aircraft. The two massive engine nacelles each housed a Pratt and Whitney R-4360-20A piston engine generating 2,975 horsepower and an Allison J33-A-10 jet engine rated at 3,825 pounds static thrust. The jet engines were to be employed for takeoff and climb with heavy payloads, and in combat situations.
The plane's weapon load was carried in a horizontal bomb bay. A great variety of ordnance was listed for the aircraft: 12 bombs up to 1,000 pounds, or six bombs up to 2,000 pounds, or 12 Mark 26 mines, or two 2,000-pound torpedoes. (Unlike the Neptune, the Mercator was not intended to carry weapons on wing pylons.) For self-defense the production aircraft, with a normal crew of nine, had twin 20-mm cannon turrets in the nose and tail, and a twin .50-caliber machine-gun turret in the dorsal position. Apparently at one point two flexible .50-caliber guns were also to be mounted in the waist position.
The first prototype XP4M-1 initially flew on 20 September 1946. The two prototypes, after a lengthy development effort, were followed by 19 production P4M-1 aircraft, completed over one year from September 1949. The early aircraft were delivered to Patrol Squadron (VP) 21, based at Naval Air Station Patuxent River, Maryland. A short time later the squadron deployed to Port Lyautey in French Morocco, a major base for U.S. naval air operations in the western Mediterranean. The Mercators suffered maintenance problems, in particular with their jet engines.3
Beyond practicing attack missions during Mediterranean operations, the Martin aircraft were primarily used as VIP transports. VP-21 flew ten of them until February 1953, when they were traded in for P2V-6 Neptunes. But the Mercator's career was not yet over.
The Navy decided to modify a number of the patrol planes for electronic reconnaissance. They were generally called "ferrets." Given the designation P4M-1Q, the aircraft were refitted at the Navy's overhaul facility at Norfolk, Virginia. The initial P4M-1Q first flew in February 1951. While retaining the large AN/APS-33A search radar in the ventral position as well as other standard electronics, the -1Q variant was laden with electronic countermeasure receivers, direction finders, pulse analyzers, and a wire recorder. The full gun armament was retained, but the crew was increased to 13 to handle the additional electronic gear, although the aircraft often flew with up to 16 men on board. It had a cruising speed of 191 mph at 1,500 feet. Cutting in two jet engines, the P4M-1Q was rated at a maximum speed of 362 mph.
The modified Mercators took over from older naval aircraft flying spy missions along the periphery of the Soviet Union, China, and North Korea. The specialized Electronic Countermeasures Squadron (VQ) 1 was established at Iwakuni, Japan, on 1 June 1955, flying -1Q aircraft; VQ-2 was established on 1 September 1955, at Port Lyautey (now Kenitra) with the same type aircraft. (The latter squadron was relocated to Rota, Spain, in 1960.)
Opposing fighters often buzzed Mercator spyplanes as they flew over international waters off the coasts of hostile countries. On 23 April 1953, two MiG-15 fighters attacked a P4M-1Q off the Chinese coast. They made several firing runs at the aircraft, with the Navy plane returning fire. None of the aircraft appeared to have suffered damage. Three years later, however, on 22 August 1956, another VQ-1 Mercator was shot down by a Chinese MiG while on a night reconnaissance flight some 30 miles off the Chinese coast near Wenchow. There were no American survivors among the crew of 16. A U.S. destroyer recovered two bodies and wreckage from the aircraft, and the Chinese government returned two other bodies. A third acknowledged attack occurred on 16 June 1959, some 50 miles east of the Korean demilitarized zone. Two North Korean MiG-17s attacked the VQ-1 aircraft, damaging the starboard engine and seriously wounding the tail gunner. The Mercator was able to land at an air base in Japan.
Another Mercator ferret crashed into the eastern Mediterranean on 16 January 1960, with the loss of all 16 crewmen. That flight, like some others by VQ-2 aircraft, was launched from Incirlik, Turkey. Unofficial reports indicate that the aircraft had strayed over the Ukraine and was chased and possibly damaged by Soviet MiG fighters. But that seems unlikely. The distance from the Ukraine to the sea is too far for a seriously damaged aircraft, and it could have landed in allied Turkey.
Regardless, the Mercator's days had been numbered and the last were retired in 1960, when both VQ-1 and VQ-2 replaced their "patrol aircraft" with A3D-1Q/2Q Skywarriors and WV-2Q Warning Stars.4
The Mercator was one of three major aircraft produced by the Martin Company for the post
World War II Navy. None of the three, however, enjoyed major success as first-line aircraft. The AM-1 Mauler, a carrier-based attack aircraft, lost out to the Douglas AD Skyraider, and the P6M Seamaster jet-powered flying boat attack/minelaying aircraft was cancelled after several prototypes flew, in part, to help pay for the Polaris submarine program. Interestingly, six Maulers flew as a "Q" variant, i.e., in the radar countermeasures configuration as the AM-1Q.These were the last of a long and generally successful line of naval aircraft produced by Martin. And they were outlasted by the firm's earlier P5M Marlin flying boat-later designated P-5
that survived in U.S. Navy service until 1967, gaining the sobriquet of being the Navy's last flying boat.1. Mercator is the term for a cylindrical projection of the Earth's surface developed by Flemish cartographer Gerhardus Mercator (1512-1594).
2. U.S. Navy, "Standard Aircraft Characteristics P4M-1 Mercator," 1 February 1952, p. 3.
3. An excellent description of the aircraft, their problems, and operations is found in Robert F. Dorr and Richard R. Burgess, "Ferreting Mercators," Air International, October 1993, pp. 215-22. Also see CDR Robert C. M. Ottensmeyer, USN (Ret.), "A Sad Day in the Cold War," Naval History, March/April 1997, pp. 37-40.
4. These aircraft were redesignated on 1 October 1962, as EA-3 and EC-121, respectively.