History
Design and Development
In 1944, the Mercator was designed as a four-engine (two props and two jets) long-range patrol bomber for the US Navy to replace the four-engine Consolidated P4Y-1/-2 Privateers. Although it was externally similar to the P2V Neptune, the Mercator was much later developed for a different requirement. Its specific design purpose was long-range patrol and laying mines during the planned 1946 invasion of Japan.
Neptune’s design work originated in 1941 when the Navy asked Lockheed to design a replacement for its successful medium-range Ventura patrol bombers. P2V was never designed with jet engines in the initial plans. However, the P2V competed as a long-range patrol aircraft instead of the medium-range patrol one, as the P2V “Truculent Turtle” managed to break the record by completing an 11,235 mile from Australia to Perth, Australia, on September 29, 1946, to Columbus, Ohio, on October 1, 1946; the record stood until 1962. The Navy decided it was content with ordering more Neptunes and relegated the P4M Mercator to a limited production run of 19 aircraft and two prototypes.
The P4M was to be powered by two 3,250-hp Pratt & Whitney R-4360-20 reciprocating engines as the primary power plants for the patrol mission. It can fly up to 16 hours without using the J33 turbojet engines in a search flight. The J33 engines were used to provide boost during takeoff combat. 20-mm cannons were installed in the Emerson nose turret and tail turret. They could fire through a 180-degree arc, either vertically or horizontally. The aircraft was designed to carry 12,000 pounds of ordnance, depth bombs, regular bombs, torpedoes, or mines.
Prototypes
On July 6, 1944, the Navy awarded Martin a contract for two XP4M-1s powered by 2,975-hp P&W R-4360-4 Wasp Majors and 3,825-lbf J33-A-17 turbojets. These turbojets were fitted in the tear of two enlarged engine nacelles behind the radial engines with the intakes beneath. Instead of retracting into the engine nacelle, the landing gear would be retracted into the wing panel outboard the nacelles. The first XP4M-1 (02789) was rolled out on June 17, 1946, and later flown for the first time on September 20, 1946, three months after the rollout. The second XP4M-1 (02790) was later built and had a mockup radar in the nose on rollout. Tests at Martin showed that the XP4M-1, with all engines at takeoff power, could outclimb any piston-engined fighters of the era up to 20,000 feet.
Production
A short production of 19 P4M-1s was ordered and completed in September 1950. The production P4M-1 appeared to be much sleeker than the XP4M-1s. The rear fuselage on the P4M-1 was lengthened, narrowed, and streamlined to allow the installation of an Emerson Aero 11B ball-and-socket tail turret. The proposed waist gun position was deleted. The first flight of P4M-1 was completed on August 31, 1949. The early Mercators were on par speed-wise with many modern fighters.
Operational Service
The Navy’s Patrol Squadron 21 was selected to operate the P4M-1 in 1949, and it was previously flying PB4Y-2s at Patuxent River, Maryland. The first P4M-1s were delivered to VP-21 in June 1950. The squadron flew the Mercators and Privateers until the last PBY-2 retired on September 5. The last P4M-1 was delivered to VP-21 on September 23, 1950. The squadron made an extended deployment to the Mediterranean and Europe to conduct exercises with the Navy fleet and NATO units. The aircraft and crews returned to Pax River in January 1952, where the Mercators were replaced by P2V Neptunes. These P4M-1s went into the overhaul at NAS Norfolk for conversion into P4M-1Q Electronic Reconnaissance Aircraft. All the production Mercator aircraft, except one lost during testing, were converted into P4M-1Qs. These aircraft received a large number of different antennas and were installed with a chin and a second bomb bay door to house the antenna. Internally, the P4M-1Q was completely rebuilt for the ECM equipment. The crew was increased from 9 to 16 to operate these ECM equipment.
After the conversion, the P4M-1Qs were released from VP-21. The P4M-1Qs of electronic countermeasures VQ-1 and VQ-2 squadrons would be flown continuously in clandestine electronic intelligence missions against China, North Korea, Russia, and Vietnam always at night until 1960. Before retirement in 1960, 7 of 19 Mercators were stricken from the service. Five were lost in accidents/mishaps, one was completely destroyed in a fatal shootdown by Chinese MiGs, and one was heavily damaged in a pursuit by North Korean MiG-17s. The lack of spares for the Mercator was another factor in their retirement.
The Douglas EA-3B Skywarrior and Lockheed WV-2Q Warning Star replaced the P4M-1Qs in the service by 1960. Unlike the Mercator, the Skywarrior was compact and flexible enough to be operated from and stored below the decks of aircraft carriers. None of the P4M-1 airframes survived after the retirement, as all the remaining aircraft were scrapped.
