Martin PB2M Mars

by Jack McKillop

The Glenn L. Martin Company

See Martin PBM.


These aircraft were the world’s largest operational seaplanes and the Navy’s largest aircraft of World War II. Both were four-engine, all-metal, high-wing monoplane flying boats with two decks and fixed stabilizing floats under the wings. The PB2M was a long-range reconnaissance bomber later converted to a transport and the JRM was built as a transport.

Production History

XPB2M-1: One prototype powered by four 2,000-horsepower Wright XR-3350-4 18-cylinder, two row, air-cooled radial engines driving reversing 16-feet, 8-inch (5.08-meter) three bladed propellers. The aircraft was armed with five 0.30-caliber (7.62-millimeter) machine guns in the bow, dorsal, tail, waist and lower rear hull. The waist and dorsal guns were in retractable turrets. This aircraft had twin PBM-type horizontal and vertical tail surfaces. This prototype had two decks for the crew of seven to 13. The officers quarters, wardroom, lavatory and the captain’s private cabin were below the flight deck The huge bomb bays were amidships under the hull beneath the wings and had two racks capable of holding five 1,000-pound (454-kilogram) bombs. The enlisted men’s quarters, mess and lavatory were located aft of the bomb bay.

XPB2M-1R: The prototype converted to a transport with all armament removed and bomb bays sealed which allowed 4,000-cubic-feet (113-cubic-meters) of space for cargo. The plane was re-engined with four 2,300-horsepower Wright R-3350-8 18-cylinder, two row, air-cooled radial engines driving reversing 16-feet, 8-inch (5.08-meter) three bladed propellers.  The floors were reinforced, hatches widened and loading equipment installed. Crew of seven.

JRM-1: Five production versions of the XPB2M-1R powered by four 2,200-horsepower Wright R3350-18 two row, air-cooled radial engines driving reversing 16-feet, 8-inch (5.08-meter) three bladed propellers. External changes were the replacement of the two vertical fins by a single 44-foot (13.41-meter) vertical fin, the bow and rear step were lengthened by about 4-feet (1.22-meters) to add cargo space and a redesign of the main and cargo hatches. Internally, a 5,000-pound (2,268-kilogram) capacity cargo hoist on an overhead track ran out 20-feet (6.10-meters) under both wings through the main loading hatches. There were two troop/cargo deck with stairways fore and aft and separate crew quarters. The interior could be configured as an ambulance aircraft for 84 stretcher cases with 25 medical attendants; a passenger transport carrying 50 in reclining chairs; or a troop transport carrying 132 seated troops. As a cargo transport, it can carry seven Jeeps or other bulky equipment. Normally, a crew of 11 flew the aircraft.

JRM-2: One aircraft with a higher gross weight and powered by four 3,000-horsepower Pratt & Whitney R4360-4 28-cylinder, four row, air-cooled radial engines which allowed it to carry an additional 12,000 pounds (5,443-kilograms) of cargo.

JRM-3: Four JM-1s re-engined with four 3,000-horsepower Pratt & Whitney R4360-4 radial engines.

Operational History

In 1935 a Request for Proposal (RAP) from the U.S. Navy for a long-range, maritime reconnaissance bomber that would be managed by a crew of 11 was presented to four aircraft manufacturers: the Boeing Aircraft Company, Chance Vought Aircraft, Consolidated Aircraft Corporation and Martin. The contract for this aircraft, designated XPB2M-1, was signed on 1 January 1939. Originally designed as a “Sky Battleship” or “Flying Dreadnought,” her keel was laid at Middle River, Maryland on 20 August 1940 and was launched on 5 November 1941. An accidental fire during taxi tests delayed the first flight until 3 July 1942.

It became obvious that the Mars was less practical as a patrol bomber than a large number of PBM Mariners. After Martin completed their flight tests on 5 October 1942, the Mars was returned to Martin and converted to a transport which was designated XPB2M-1R. Flight tests of this aircraft began on 5 May 1943 and ended with a 33-hour endurance flight in October. The Navy accepted the XPB2M-1R at Naval Air Station (NAS) Patuxent River, Maryland on 27 November 1943 and it was assigned to Air Transport Squadron Eight (VR-8) of the Naval Air Transport Service (NATS). VR-8 was the four-engine seaplane training unit. On 30 November, the Navy flew their first Mars mission carrying a payload of 13,000-pounds (5,897-kilograms) for 4,375-miles (7,041-kilometers) from NAS Patuxent River to Naval Air Facility Natal, Brazil in 28 hours 25 minutes. The take off weight was 148,500-pounds (67,358-kilograms). On part of the return flight, a 35,000-pound (15,876-kilograms) load was carried. In March 1944, she was reassigned to VR-2 based at NAS Alameda, California and began flights between NAS Alameda and NAS Honolulu, Territory of Hawaii. Early in 1944, she flew a 4,700-mile (7,564-kilometer) round trip from Alameda to Honolulu in 27 hours 26 minutes carrying 20,500-pounds (9,299-kilograms) of cargo. After 78 flights, the Mars was returned to Martin overhaul and training but by the end of May 1945, the XPB2M-1R had returned to NAS Patuxent River assigned to VR-8.

On 27 June 1944, the Navy ordered 20 more transport aircraft designated JRM-1 Mars. As the war ended, the order was amended to five JRM-1s and a JRM-2. On 27 July 1945, the first JRM-1, christened Hawaii Mars, was completed but was destroyed in a landing accident in Chesapeake Bay on 5 August 1945 when the leading edge of the vertical stabilizer failed at 6,000-feet (1,829-meters)..

The remaining four JRM-1s were all delivered the first half of 1946 and the JRM-2 was delivered in 1948. All were named for Pacific Island Groups and all were assigned to VR-2 at NAS Alameda. The five aircraft were:
JRM-1, BuNo 76820: Philippine Mars.
JRM-1, BuNo 76821: Marianas Mars
JRM-1, BuNo 76822: Marshall Mars
JRM-1, BuNo 76823: Hawaii Mars
JRM-2: BuNo 76824: Caroline Mars

Marshall Mars made a forced landing in Keehi Lagoon, Oahu, Territory of Hawaii on 5 April 1950 with an engine fire. The crew were rescued after which aircraft exploded.

The remaining four aircraft were operated by VR-2 until January 1957 when they were removed from service and“beached” at NAS Alameda. In 1959, the U.S. Navy put the four Mars flying boats up for auction and they were purchased by a Canadian company and all were flown to Canada in the summer of 1959 to be used as aerial tankers against forest fires.

Survivors On Display In The U.S.

In July 2013, the following article appeared in the Alberni Valley News in Port Alberni, British Columbia, Canada:

The retired Philippine Mars seems to also be in government limbo. The Coulson group announced three years ago that the retired aircraft was being donated to the Naval Aviation Museum in Pensacola, Florida.

The plane was even repainted its original blue last year in anticipation of retirement at the museum. However, when it will be delivered remains unknown. "It has to be signed off by the White House," Coulson said. "This is such a high profile asset and there hasn't been a trade since 1992 because of problems internally in the government." Coulson explained his group is supposed to get some ex-military assets in exchange for the Philippine Mars, but wouldn't elaborate on what it is or what it would be used for, citing it's still in negotiation. Add the fact that a Canadian company is trying to get those ex-military assets, and even more bureaucracy ensues, Coulson said.

"I didn't know there were so many lawyers in Washington D.C. and how every government department has its own lawyers," Coulson said. "It's a work in progress."

Coulson added he doesn't think the Philippine Mars will be leaving this year.

BuAer Numbers

76820-76823........JRM-1 converted to JRM-3


Wing Span: 200-feet (60.96-meters)
   XPB2M-1: 117-feet 3-inches (35.74-meters)
   JRM-1/2/3: 120-feet 3-inches (36.65-meters)
Height (on beaching gear)
   XPB2M-1: 38-feet 5-inches (11.71-meters
   JRM-1/2/3: 44-feet 7-inches (13.59-meters)
Loaded Weight
   XPB2M-1: 144,000-pounds (65,317-kilometers)
   JRM-1: 148,500-pounds (67,358-kilograms)
   JRM-2/3: 165,000-pounds (74,843-kilograms)
Maximum Speed
   XPB2M-1: 224 miles per hour (360 kilometers per hour)
   JRM-1/2/3: 238 miles per hour (383 kilometers per hour)
   XPB2M-1: 4,375-miles (7,041-kilometers)
   JRM-1: 5,800-miles (9,334-kilometers)
   JRM-2/3: 6,750 miles (10,863-kilometers)