Martin P4M-1 Mercator Operated By Patrol Squadron VP-21
The Mercator and Me
By LCDR John A. Williams. USN (Ret.)
Mercator, a name out of the past. but not quite as far back as 1568. That year Gerardus Mercator produced a chart in which the parallels (latitudes) and meridians (longitudes) were at right angles. It became known to navigators, sea and air alike. as the “Mercator Projection”.
The Mercator I am familiar with is not much over fifty years old. This Mercator in my mind is a rare and exotic bird. Mercator was the name given to the fourth Navy patrol plane accepted from the Martin Aircraft Company for full time operations with the fleet air arm. Thus the letter/number designation. P4M.
The P4M Mercator was a rare “bird” because only 21 were produced between 1946 and late 1949. Of these 21, two were proto type. XP4M-1s and only 19 were ever delivered to the Navy in 1949 and 1950.
In my mind the Mercator, was also an exotic “bird”. One definition I found for exotic was “having the charm or fascination of the unfamiliar; strangely beautiful and enticing”. In this author’s opinion that makes the Mercator both rare and exotic. Very few were produced and none survived much longer then ten years. They were unfamiliar, beautiful, and just loaded with fascinating features years ahead of any other designed aircraft.
In late 1948 I received my first introduction to the Mercator. It was one of the proto type XP4Ms that had been transferred to NATTC Memphis for technical training. As I stood on the aircraft parking ramp at NATTC, it almost looked like the “back lot” of some Hollywood studio that had been producing WW II Navy aviation movies. Lots of old Navy aircraft, many familiar to me , but there it was, an almost new Mercator. At first it appeared like a Neptune but larger.
I soon learned it was radically deceptive in makeup and much superior in flight performance. It was also in late 1948 I came across the December issue of Aero Digest. It was a special Air Navy issue, volume #57, number six. I still have that old “dog-eared” copy, almost 50 years later.
On page 80 they ran a brief article on the Martin P4M. With only a few paragraphs, one picture, one drawing, but a load of information. As I was an Aviation Machinist’s Mate I was most interested in the power plants. Even with my experience with Pratt&Whitney R-183Qs (PBYs) and the PW R-2800 (P3Ms), I could not imagine the “Wasp Major” R-4360.
Then there was the Mercator’s other engines, JETS, two Allison J-33A centrifugal-flow turbojets. I mention these jets as centrifugal-flow as opposed to later axial-flow jets. The former presented a much larger frontal area, similar to the comparison of the radial reciprocating engine to the inline engine. Because of the jet’s size they were housed in the nacelle behind the R-4360. The jets added to patrol aircraft later were of the axial-flow type and. hung from pylons on the wings.
The space in the nacelle occupied by the Mercator’s jets was that of the main landing gear on the Neptunes. Thus the P4M main landing gear retracted outboard up into a slight wing cavity, similar the PB4Y or B-24.
My next sighting of a Mercator was in July 1951 at NAS Sand Point, Seattle. I was preparing to ferry a PBY-5A from O&R back to NARTU Memphis. There on the ramp were several P4M-1s assigned to Patrol Squadron Twenty-one. The planes and crews were on a round trip of the perimeter of the 48 states, and preparing for their last leg home to NAS Patuxent River, MD. On their flight from NAS San Diego to NAS Alameda the elapsed flight time was a record one hour and 15 minutes.
In September 1952 I received orders to Patrol Squadron 21, a most welcome set of orders. Until now my experience in patrol aircraft had been seaplanes, PBMs, and PBY-5A amphibian. The thought of land plane patrol aircraft had meant flying in PB4Y or P2V aircraft, neither of which I particularly cared for. Now I would soon be flying in the Mercator. After about 700 hours crew time in the PBM, I would be back in a Martin aircraft, with jets too.
Checking in to VP-21 gave me the first real close look at the Mercator, inside and out. I had anticipated going right on a flight crew. Not so ! To be a P4M plane captain, or even his second mech, meant months of study and training.
My first month in the squadron I was assigned to engine buildup crew, night maintenance. The R4360 was awesome, 28 cylinders in all, and I could see its nickname the “corn-cob”. That first month, I must have done something right because the next month I got on a flight crew, in training.
Now I began to realize the many advanced features of the Mercator. The jets were just what seemed most important from a power standpoint. The pilots compartment vias raised with a semi-bubble canopy for increased vision. The after station had a large “picture” window on either side for improved sea search quality. The radio and radar stations were across the flight deck isle from each other and of course the overhead was high enough for the crew to stand upright. Just aft of this compartment was the radar countermeasures operator (RCM) station, later changed to electronics countermeasure (ECM). An upper !escape hatch was located in this area. In fact the Mercator had several well designated ditching and escape features. One such ditching feature was a “hydro-flap”. Actually it was the nose entrance hatch. This hatch could be lowered in flight just prior to ditching. When locked down in a position of 45 degrees it was beefed up to withstand a 10,000 pound load.
For defensive firepower the P4M had twin 20 millimeter cannon in both the nose and tail turrets. The upper deck turret was the standard Martin 250CE, two 50 caliber, electric driven, 360 degree azimuth turret.
By my first months end of in flight training, I had flown 19 operational and training flights for a total of 75 hours. This was accompanied by ground classes on non-flying days studying all the aircraft systems, and emergency procedures. By February 1953 I had passed both oral and written exams, and all requirements for P4M-1 plane captain. I now had 166.3 flight hours, and after another month of flight checks, I received my official P4M-1 plane captain card #42 on 16 March 1953.
Patrol Squadron Twenty-one had a primary mission of “high speed aerial mine delivery”, with a secondary in ASW. For this reason the Mercator did not have the AN/APS-20 search radar of the Neptune with its large radome, but the AN/APS-33 and smaller radome. On routine training flights the jets were not used for power, however they were always at idle for take off and landing as a matter of safety. Occasionally there would be a full power, 2 turning- 2 burning, take off, and that would through you back in your seat, near catapult force.
In February 1953 VP-21 began to receive the Lockheed P2V-6 as a replacement for the P4M. I continued to fly as P4M plane captain, and on 6 April 1953 I flew on the last P4M (BuNo 124368) flight in VP-21. These last days of my Mercator association were also spent cross training as plane captain on the P2V-6 (sans jets).
The Mercator summary, 2 proto types, 19 fleet aircraft. One Mercator crashed in Chesapeake Bay March 1951 while attached to Naval Air Test Center, Pax River. Nine were delivered to VP-21. All other Mercators were converted to P4M-1Qs before leaving the Martin Plant and were assigned to VW or VQ squadrons. Eventually all VP-21’s Mercators were converted to P4M-1Qs at O&R Norfolk and sent out to VQ squadrons. These squadrons continued to operate the Mercators through the 1950s. The last ones were lost at sea, scrapped, or struck off by mid 1960. There were no survivors!
A postscript: The VP-21 P4M was replaced by another “limited issue” patrol aircraft, the P2V-6, only 67 were produced. There were also 16 P2V-6Bs, these were later designated 6Ms. But hey, this might be another story.