The Lockheed P2V Neptune

   LOCKHEED P2V-2 NEPTUNE:
   _____________________   _________________   ___________________________
 
   spec                    metric              english
   _____________________   _________________   ___________________________

   wingspan                30.5 meters         100 feet
   length                  23.8 meters         77 feet 10 inches
   height                  3.6 meters          28 feet 1 inch

   empty weight            15,400 kilograms    33,960 pounds
   max loaded weight       28,605 kilograms    63,080 pounds

   maximum speed           515 KPH             320 MPH / 278 KT
   cruise speed            287 KPH             178 MPH / 155 KT
   service ceiling         7,925 meters        26,000 feet
   range                   6,410 kilometers    3,980 miles / 3,460 NMI
   _____________________   _________________   ___________________________

* Two of the P2V-2s built were specially fitted for arctic operations and designated "P2V-2N". They were given ski landing gear that wrapped around their tires, allowing the aircraft to land on either snow or a conventional runway. The landing gear was retractable, with the skis neatly faired into the nose and the engine nacelles in flight.

The P2V-2Ns were intended for long-range arctic search and rescue, and had all armament removed, as well as the tail skid. They carried a primitive magnetic anomaly detector (MAD) probe in the tail in place of the tail turret.

At least three P2V-2s were specially modified for photo mapping duties. The solid nose containing cannon was replaced by a glassed observation nose containing a mapping camera. All armament except for the dorsal turret was removed. Other P2V-2s were modified for training and other duties, and some were even refitted with four-bladed propellers.

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[4] P2V-3 / P2V-4

* The "P2V-3" was very similar to the P2V-2, but featured even more powerful Wright R-3350-26W engines, with 3,200 horsepower for take-off. The P2V-3 was otherwise generally indistinguishable from its predecessor. With the uprated engines, the P2V-3 had a top speed of 545 KPH (338 MPH).

The first P2V-3 flew on 6 August 1948. A total of 83 were built, including subvariants, with the last delivered in January 1950. When Communist North Korea invaded South Korea later that year, the P2V-3 was pressed into service as a ground attack aircraft, plastering North Korean columns with 20 millimeter fire and HVAR volleys.

In addition to the main production version of the P2V-3, there were four subvariants:

• The "P2V-3B" special armament aircraft. There were a total of 16 P2V-3Bs, all conversions of other P2V-3 models. The P2V-3B was fitted with the ASB-1 Low Level Radar Bombing System, which was also used on the Douglas A-3 Skywarrior.

• The "P2V-3W" early-warning aircraft. 30 P2V-3Ws were built in all, and featured an APS-20 search radar, mounted in a big radome under the forward fuselage.

• The "P2V-3Z" armed transport. Two P2V-3Zs were built as specialized armed transports to carry VIPs in combat zones. They included comfortable passenger accommodations and were heavily armored. The nose cannon, dorsal turret, and most combat avionics were removed, and they were also fitted with four-bladed propellers. Both P2V-3Zs were used operationally during the Korean War.

• The "P2V-3C" carrier-launched aircraft. Eleven P2V-3Cs were built to provide the US Navy with a carrier-launched nuclear strike capability. These aircraft were fitted them with eight 450-kilogram (1,000-pound) thrust JATO bottles under the rear fuselage.

  Unsurprisingly, there was no provision for carrier recovery. Getting such a big aircraft off a carrier deck was impressive when the Neptune hadn't been designed to do such a thing to begin with, and landing it on a carrier would have been quite a trick. The aircraft was to fly to a friendly base after dropping its nuclear weapon, or ditch near a Navy vessel.

  The P2V-3C was stripped of nose armament, dorsal turret, HVAR stubs, belly radome, astrodome, and tail skid. Additional fuel tanks were installed. Several P2V-3Cs set records for carrier-launched aircraft in 1948 and 1949.

* The "P2V-4" was another stepwise refinement of the Neptune type, featuring yet another uprated powerplant fit, increased fuel capacity, and standard fit of the APS-20 radar and associated enlarged radome used on the P2V-3W. The first P2V-4 flew on 14 November 1949.

The new powerplants were Wright R-3350-30W Turbo-Compound engines with 3,750 horsepower each, though early production aircraft had the R-3350-26W engines used on the P2V-3 and were upgraded to the new engines later. All the P2V-4s used four-bladed propellers. The top speed increased once more, to 565 KPH (350 MPH).

The additional fuel tanks fitted to the P2V-1 TRUCULENT TURTLE for its record breaking distance flight led Lockheed engineers to consider what might be done to improve the fuel capacity of the Neptune in general, and the P2V-4 incorporated additional fuel tanks in the fuselage and wings. It also featured spindle-shaped external tanks that were attached under the wing tips. The external tank attached to the right wingtip included a searchlight in its nose. The increased fuel capacity gave the P2V-4 a range of 6,750 kilometers (4,200 miles).

Armament fit of the P2V-4 was the same as that of the standard P2V-3. It carried radio sonobuoys to improve its antisubmarine capabilities, and was known as the "Snorkel Snipper" since its likely prey was to be diesel submarines operating with snorkels. Crew was increased to eight to include a sonobuoy operator.

52 P2V-4s were built. There were no formal subvariants. Some P2V-4s were used for ocean patrol during the Korean War. In 1962, the US military changed to a uniform aircraft designation system, and P2V-4s still in operation with the US Naval Reserve were redesignated "P-2Ds".

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[5] P2V-5

* The "P2V-5" was the definitive Neptune variant, with 424 built, and replaced earlier Neptune variants in first line operation, relegating them to reserve status. Various changes and enhancements made through its subvariants resulted in an aircraft distinctly different in appearance from the earlier variants that would set a pattern for later variants.

The first P2V-5 flew on 29 December 1950, and the type performed ocean patrols during the later parts of the Korean War. The P2V-5 retained the same powerplants as the P2V-4, but the six fixed 20 millimeter guns in the nose were replaced by an Emerson nose turret mounting twin 20 millimeter guns. Additional anti-submarine warfare (ASW) and electronics countermeasures (ECM) gear were incorporated, and another crew member was added to operate the new ASW-ECM gear, bringing the total to nine.

The wingtip tanks introduced in the P2V-4 were enlarged and attached directly to the wingtips, rather than under them, though initial production retained the earlier tanks. Range was increased to 7,650 kilometers (4,750 miles).

The bigger tanks had fins and could be dropped in an emergency. The right wingtip tank had a searchlight in front whose movement was synchronized to and boresighted with that of the nose turret. Apparently one of the wingtip tanks was also fitted with a short-range radar, variously given as the APS-8 or APS-31, and either fitted in the nose of the left wingtip tank or ganged to the searchlight in the right. In any case, the P2V-5 retained the APS-20 search radar of the P2V-4.

The P2V-5 was upgraded with new features during production, such as:

• A raised cockpit with bigger windscreens for improved visibility.

• A clear glass observation position that replaced the nose turret.

• A long ASQ-8 MAD stinger that replaced the tail turret.

One of the most distinctive updates was a refit with two 1,540-kilogram (3,400-pound) thrust Westinghouse J34-WE-34 turbojets, fitted outboard of the piston engines. These turbojets were used to assist in take-offs and for additional combat speed. The number of HVAR stub launch rails was reduced from 16 to 8 when the turbojets were fitted. This subvariant was designated the "P2V-5F".

   LOCKHEED P2V-5F NEPTUNE:
   _____________________   _________________   ___________________________
 
   spec                    metric              english
   _____________________   _________________   ___________________________

   wingspan                31.7 meters         103 feet 10 inches
   length                  27.8 meters         91 feet 2 inches
   height                  3.6 meters          28 feet 1 inch

   empty weight            18,935 kilograms    41,755 pounds
   max loaded weight       34,535 kilograms    76,150 pounds

   maximum speed           520 KPH             323 MPH / 280 KT
   cruise speed            333 KPH             207 MPH / 180 KT
   service ceiling         7,705 meters        23,200 feet
   range                   7,650 kilometers    4,750 miles / 4,130 NMI
   _____________________   _________________   ___________________________

There was also a "P2V-5FE", which was fitted with additional avionics, exactly what is unclear, and a "P2V-5FS" which carried the "Julie/Jezebel" sonar system. Some P2V-5Fs were stripped of all armament and used as US Navy "hurricane hunters", flying into hurricanes to perform weather observations.

The British RAF Coastal Command received 52 P2V-5s in 1952. After four years in British service, these aircraft were passed on by various paths to the Netherlands, Portugal, Argentina, Brazil, and Australia.

In the 1960s, the P2V-5 and P2V-5F were redesignated "P-2E". The subvariants were redesignated as follows:

• P2V-5FD: DP-2E
• P2V-5FE: EP-2E
• P2V-5FS: SP-2E

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[6] P2V-6 / P2V-7

* The "P2V-6" was essentially a P2V-5 with different electronic equipment fits for mine-laying and antisubmarine warfare, and resembled the P2V-5. The P2V-6 reverted to the Emerson nose turret with twin 20 millimeter guns, and featured an APS-70 (some sources state APS-33) rather than an APS-20 radar and a smaller radome.

83 P2V-6s were built in 1952 and 1953. There were a number of subvariants, including:

• The "P2V-6B", later redesignated "P2V-6M", was fitted to carry the Fairchild Petrel AUM-N-2 antisubmarine missile, which was a winged booster carrying a homing torpedo.

• The "P2V-6F" was a field retrofit with twin J-34-WE jet engines, like the P2V-5F.

• The "P2V-6T" was a trainer, with all armament and wingtip tanks deleted.

In the 1960s, the surviving P2V-6s and P2V-6Fs were redesignated the "P-2G". The P2V-6M was redesignated the "MP-2F", and the P2V-6T was redesignated the "TP-2F".

* The last US-built model of the Neptune was the "P2V-7", with yet another uprated Wright radial, the R-3350-32W Turbo Compound Cyclone engine, with water-methanol injection and 4,000 horsepower for take-off. The P2V-7 was the first Neptune to have J-34 turbojet engines fitted on the production line, as opposed to retrofitted in the field.

The P2V-7 had a distinctive enlarged canopy with a better all-round view, and a longer fuselage. Wingtip tanks were streamlined and made smaller. Early production had nose, tail, and dorsal turrets, but these were quickly eliminated in favor of a clear nose, MAD boom, and observer dome respectively. The P2V-7 reverted to the APS-20 radar used on the P2V-5, with its large radome, though the radome was mounted farther forward.

   LOCKHEED P2V-7 NEPTUNE:
   _____________________   _________________   ___________________________
 
   spec                    metric              english
   _____________________   _________________   ___________________________

   wingspan                31.7 meters         103 feet 10 inches
   length                  28.0 meters         91 feet 8 inches
   height                  3.6 meters          28 feet 1 inch

   empty weight            19,505 kilograms    43,010 pounds
   max loaded weight       36,300 kilograms    80,000 pounds

   maximum speed           586 KPH             364 MPH / 316 KT
   cruise speed            300 KPH             188 MPH / 165 KT
   service ceiling         6,830 meters        22,400 feet
   range                   7,000 kilometers    4,350 miles / 3,735 NMI
   _____________________   _________________   ___________________________

Some 359 P2V-7s were built in all, beginning in 1954, including 48 built by Kawasaki in Japan for the country's Self-Defence Forces. P2V-7s were also operated by Canada, Australia, France, the Netherlands.

The type was redesignated "P-2H" in the 1960s. The P2V-7S became the "SP-2H", and the P2V-7LP became the "LP-2J".

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[7] SPECIAL MISSION NEPTUNES

* There were a number of interesting modifications of the Neptune during its career, and some of these modifications were operated by the US Air Force (USAF) and US Army.

Seven P2V-7s were built specifically for the USAF for electronic intelligence (ELINT). These black-painted aircraft were designated "RB-69A", though they had a secondary Navy designation of "P2V-7U". They often featured a side-looking airborne radar (SLAR) antenna attached on the fuselage from behind the wing to in front of the horizontal tailplane.

The activities of these "black" aircraft remain obscure, but apparently they were used to penetrate Chinese and Soviet airspace on ELINT "ferret" missions. The US Navy also operated three P-2Hs (P2V-7) that were modified to a similar configuration.

* A number of P-2Es (P2V-5Fs) were modified as ELINT aircraft, with appropriate electronics equipment, and redesignated "AP-2E". The Army operated them out of Cam Rahn Bay from the summer of 1967 to the spring of 1972. The AP-2E still very much looked like a Navy Neptune, but other Vietnam modifications were more drastic.

* The Navy "OP-2E" was a highly modified P-2E (P2V-5F) with antisubmarine avionics, the APS-20 radome, and MAD tailboom removed, giving it an odd bobtailed appearance. There were twelve such modifications, with the aircraft refitted with a chin radome and a camera pack under the tail; armed with 7.62 millimeter "minigun" pods under the wings, along with provisions for mounting a machine gun in a window on either side of the rear fuselage; and painted jungle green.

The OP-2Es operated out of Thailand between the fall of 1967 and the summer of 1968, where they dropped sensors on the Ho Chi Minh Trail as part of the IGLOO WHITE operation to block North Vietnamese movement over the Ho Chi Minh Trail into South Vietnam.

* The "AP-2H" was an even more drastic modification, of a P-2H (P2V-7), for use as a night and all-weather gunship. Like the OP-2E, the AP-2H had their search radar radome and MAD stinger removed, but the stinger was replaced with an Aero 11/A turret with twin 20 millimeter cannon.

The AP-2H was fitted with a chin blister containing a low light level TV (LLLTV) camera, along with a pod for APQ-20 radar mounted just behind the nosewheel doors. The type apparently carried other sensors, as well as ground-attack armament such as 40 millimeter grenade launchers and miniguns.

These aircraft were operated by the Navy over Southeast Asia from the fall of 1967 to the late spring of 1969, dropping IGLOO WHITE sensors, plus bombs and napalm.

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[8] P-2J / END OF THE ROAD

* The very last version of the Neptune was the Japanese-built "P-2J" (originally P2V-KAI, where "KAI" means "kaizen" or "modification"), and was apparently something of a dinosaur. Work on the P-2J was begun in 1961, when the type was clearly obsolescent, and the first P-2J didn't fly until 1966. The last of 89 P-2Js was delivered in 1979.

The P-2J was essentially ten years behind the times, despite attempts to make improvements on the basic aircraft. The Wright radial engines were replaced with Japanese-built copies of the GE T64-IHI-10 turboprop engines, with each engine providing 2,850 horsepower and driving three-bladed propellers. The booster turbojets were also Japanese copies of American engines, with the designation IHI-J3. Each turbojet offered 1,400 kilograms (3,085 pounds) thrust. With the new powerplants, the P-2J had a top speed of almost 650 KPH (403 MPH).

The P-2J was stretched to accommodate 12 crewmen, and the tail surfaces were enlarged and their shape modified. APS-80 search radar was fitted, resulting in a still smaller radome. Updated avionics systems were installed, and these systems were much more compact than those used in other versions of the Neptune. The lighter avionics load permitted greater fuel capacity. The turboprop nacelles were too tight to accommodate the big main landing gear tire used on other Neptunes, and so the P-2J's main gear was fitted with two wheels each.

The use of local technology simply made for a more expensive aircraft, and the turboprop engines saved weight but increased fuel consumption. The P-2Js were phased out in the 1980s in favor of the Orion, which eventually replaced the Neptune in the ocean-patrol air fleets of the West.

* A total of 1,188 Neptunes were built in all. The aircraft was highly successful and had a long and productive lifetime.

Although out of service with military air arms, the Neptune has proven popular as a "fire bomber", fitted with tanks of fire retardant for fighting range and forest fires. The US Forest Service operated one for a time, and a number of Neptunes have been operated by various fire-fighting companies. In particular, four were modified and are still operated by Aero Union of California, and are known as "Firestars".

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[9] FOOTNOTE: THE MARTIN P4M MERCATOR

* The Neptune had a rival of sorts. The Martin "P4M Mercator" was somewhat similar to the Neptune, if about 50% heavier, and also intended for the maritime patrol mission. It ended up being overshadowed by the Neptune, was only built in small quantities, and found its niche as a spyplane rather than a patrol aircraft.

At the outset, the two types of aircraft did not seem to be in direct competition. As noted, Lockheed had been considering a follow-on to the Hudson-Ventura family of medium patrol aircraft as far back as 1941, with commitment to development of the Neptune in early 1944.

In contrast, the Martin "Model 219" was conceived in early 1944 as a replacement for the Consolidated PB4Y Privateer, the "navalized" version of the B-24 bomber. The Mercator was to be a long-range patrol aircraft whose primary role was envisioned as minelaying, in support of the planned invasion of Japan. The Navy awarded a contract for the development of two "XP4M-1" prototypes on 6 July 1944.

The Neptune was a smaller and simpler aircraft, and Lockheed had spent several years in preliminary design before the Navy committed to the type. As a result, Neptune development was straightforward and rapid, with the first prototype flying in the spring of 1945. Martin, lacking the benefit of such a head start, didn't get the first of the two XP4M-1 "Mercator" prototypes into the air until 20 September 1946, with Martin's chief test pilot, O.E. "Pat" Tibbs at the controls.

The war was over by this time, and the cheaper Neptune seemed to be well able to fulfill most of the roles for which the Mercator was designed. In addition, Martin did little to promote the type, giving it low priority in the company's efforts. However, for whatever reason the Navy order 19 production "P4M-1" Mercators, with the first rolled out on 18 July 1949.

The production P4M-1 Mercator was a big aircraft. It was of more or less conventional configuration, with a long wing mounted in mid-fuselage and a conventional tail assembly, but it did have some unusual features. It appeared to be a twin-engined aircraft, powered by twin Pratt & Whitney (P&W) R-4360-20A 28-cylinder, 4-row piston engines, each driving a broad four-bladed variable-pitch propeller, though the prototypes had experimented with a three-bladed propeller.

However, the engine nacelles also included an Allison J33-A-10A centrifugal flow turbojet engine in the rear, a copy of the British de Havilland Goblin engine. There was an intake scoop in the bottom of each nacelle behind the P&W piston engine that could be closed during cruise flight, when the engines were off.

The nosewheel retracted backwards, while the main gear hinged up into the wings outboard of the engines. All the gear assemblies had single wheels. In another unusual feature, as the wing was too thin to accommodate the big main-gear wheels, they retracted into fairings that didn't have doors, leaving the wheel visible in flight. The wing was divided into two sections with different airfoil cross-sections, the inboard section providing high lift and the outboard section optimized for fast cruise. This scheme was apparently effective, but it did give funny stall characteristics, because the outer section would stall before the inner section.

   MARTIN P4M-1 MERCATOR:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                34.77 meters        114 feet 1 inch
   length                  25.6 meters         84 feet
   height                  7.95 meters         26 feet 1 inch
   max loaded weight       40,085 kilograms    88,375 pounds

   max speed at altitude   660 KPH             410 MPH / 355 KT
   service ceiling         10,550 meters       34,600 feet
   range                   4,570 kilometers    2,840 MI / 2,470 NMI
   _____________________   _________________   _______________________

Yet another unusual feature of the Mercator was its bombbay, which borrowed from British practice in being wide and shallow, rather than narrow and deep as was the American tradition. This permitted greater flexibility in munitions drops and also meant a roomier aircraft. Possible weapons fits included twelve 275 kilogram (610 pound) depth charges; two Mark 13-3 torpedoes; twelve 450 kilogram (1,000 pound) mines; or six 900 kilogram (2,000 mines). The bombbay could also be fitted with four auxiliary fuel tanks for long-range patrol or ferry flights. There was no provision for external stores.

The Mercator was fitted with APS-33 search radar, with a radome mounted under the rear fuselage. There was also a smaller antenna dome forward of the bombbay, which may have been for short-range targeting radar. The aircraft carried a crew of nine, including pilot, copilot, navigator, radio operator, radar operator, countermeasures operator, camera operator, and two dedicated gunners. The aircraft was roomy and comfortable, with a galley and a head, both pleasant features for long-range patrols.

* The Mercator's life as a patrol aircraft was short. After delivery of the first ten production aircraft, the Navy decided that the type's capacity and good performance would make it an excellent ELINT aircraft, and the last nine were converted to "P4M-1Q" ELINT aircraft immediately following factory delivery. The conversions were performed by the Navy at Norfolk, the first of P4M-1Qs flying in February 1951. The eight surviving Mercators were also rebuilt to P4M-1Q standards.

The P4M-1Q was littered with antennas for ELINT receivers, and the crew was increased to 14, later 16, to operate the ELINT gear. The P4M-1Q was substantially heavier than the P4M-1, resulting in a smaller radius of action and possibly a lower service ceiling. The additional weight of the ELINT gear was also not well distributed over the aircraft and affected its handling, particularly when most of the fuel had been burned off.

However, the P4M-1Q proved very useful in its role, skirting outside the borders of the Soviet Union and other hostile states to "sniff" radar emissions. The operations of the type were a deep black secret, with aircraft given false or purely fictitious markings. A commander of a conventional Navy squadron saw a Mercator with the markings of his own unit, demanded to know what was going on, with the crew replying as tactfully as they could that they couldn't tell him.

Armament was gradually removed from ELINT Mercators, until one was jumped by Chinese MiGs in the dark hours of the morning of 22 August 1956. The aircraft was shot down, with all the crew killed. The guns were hastily refitted to the surviving Mercators. A Mercator was bounced by North Korean MiGs on 16 June 1959 in international airspace. The spy aircraft fought back well enough to hold off the attackers until help arrived, though one crewman was badly wounded and the Mercator was written off after landing.

Several other Mercators were lost in accidents. Between attrition and lack of spares, by 1960 the type could no longer be kept in operation, and the last Mercators were withdrawn from service in July 1960. All were scrapped and none survive.

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[10] COMMENTS, SOURCES, & REVISION HISTORY

* Sources include:

• P2V NEPTUNE IN ACTION by Jim Sullivan, Squadron/Signal Publications, 1985.

• THE LOCKHEED P2V NEPTUNE by Holmes G. Anderson, Profile Publications.

• MODERN WARPLANES by Doug Richardson, Salamander Books, 1982.

• "Martin P4M Mercator" by John Lake & Robert F. Dorr, WINGS OF FAME, Volume 19, 2000, 138:149.

One of my colleagues worked on the Neptune as an avionics tech in the early 1960s, and provided me with the PROFILE publication on the subject. He was a little startled to find out that Neptunes had been operated off carriers. I imagine that would have been interesting to watch. He also had an interesting story about crawling forward through the tunnel over the top of the Neptune's weapons bay when the pilot decided to cut the booster jets. He left the tunnel a little faster than he planned on.

The v1.0 version of this document left much to be desired, and in fact I considered scrapping it. Fortunately, I managed to find the book P2V NEPTUNE IN ACTION in a local hobby shop and used that to create the much improved v2.0 version. I was lucky to find the book, since it was clearly out of print, with its paper faded yellow around the edges.

* Revision history:

   v1.0   / 01 oct 97 / gvg
   v2.0   / 01 may 99 / gvg / Major rewrite and expansion.
   v2.1.0 / 01 feb 02 / gvg / Cleaned up, added section on Mercator.