The Martin JRM Mars was the largest flying boat ever to enter production although only 6 were built. The U.S. Navy contracted the development of the XPB2M-1 Mars in 1938 as a flying dreadnought for ocean patrol.

Navy service

The Martin Company effectively scaled up their successful PBM Mariner patrol bomber design to produce the prototype XPB2M-1 Mars. After flight tests with the XPB2M between 1941 and 1943, she was passed on to the Navy. The original patrol bomber concept was considered obsolete by this time, and the Mars was converted into a transport aircraft designated the XPB2M-1R. The Navy was satisfied with the performance, and ordered 20 of the modified JRM-1 Mars. The first, named Hawaii Mars, was delivered in June 1945, but the with the end of World War II the Navy scaled back their order, buying only the five aircraft which were then on the production line. Though the original Hawaii Mars was lost in an accident on Chesapeake Bay, the other 5 Mars were completed, and the last delivered in 1947.

Named the Marianas Mars, Philippine Mars, Marshall Mars, Caroline Mars, and a second Hawaii Mars, the 5 production Mars aircraft entered service ferrying cargo to Hawaii and the Pacific Islands. The last production airplane (the Caroline Mars) was designated JRM-2, powered by 3,000 hp Pratt & Whitney R-4360 engines, and featured a higher maximum weight and other improvements. On 5 April, 1950, the Marshall Mars was lost near Hawaii when an engine fire consumed the airplane after her crew had evacuated. The remaining "Big Four" flew record amounts of Naval cargo on the San Francisco-Honolulu route efficiently until 1956, when they were parked at NAS Alameda.

Variants

• XPB2M-1R Bu. 1520 (c/n 877) The Old Lady. Conversion of the XPB2M-1 to Long range cargo transport with the armament removed, installation of additional cargo hatches and cargo loading equipment, existing hatches were enlarged and the decking was reinforced. Delivery date: 31 December 1943, first flight 3 July 1942. Assigned initially to VR-8 (Patuxent River) for crew training and was later transferred to VR-2 (NAS Alameda). Scrapped 1945.

• JRM-1 Bu. 76819 - 76823 (c/n 9263 - 9267). Originally 20 aircraft ordered - production reduced to 6. Long range cargo transport. Martin model 170a. Single-tail design, and having a longer hull with fewer bulkheads and a larger maximum take-off weight. It had also been fitted with equipment for overhead cargo handling and was powered by four Wright R-3350-24WA Cyclone engines with 4-bladed propellers.

• • JRM-1 Bu. 76819 (c/n 9263) Hawaii Mars. First flight: 21 July 1945, Sank: 5 August 1945 - Chesapeake Bay; disposed for scrap.

• • JRM-1 Bu. 76820 (c/n 9264) Philippine Mars. Delivery date: 26 June 1946. Assigned to VR-2 (Alemeda NAS). SOC: 22 August 1956. Sold 1959. Converted to forest fire fighting aircraft. Registered CF-LYK (later C-FLYK) - still flying with Coulson Group at Sproat Lake, B.C.

• • JRM-1 Bu. 76821 (c/n 9265) Marianas Mars. Delivery date: 26 February 1946. Assigned to VR-2 (Alemeda NAS). SOC: 22 August 1956. Sold 1959. Converted to forest fighting aircraft. Registered CF-LYJ - Crashed into Mount Moriarty near Nanaimo Vancover 23 June 1961 killing crew of 4. Water drop mechanism failed, leaving aircraft unable to climb quickly enough to clear mountain.

• • JRM-1 Bu. 76822 (c/n 9266) Marshall Mars. Destroyed by engine fire, sank 5 April 1950 - Diamond Head, Oahu (Pilot: LCDR Glenn E. Simmons) 

• • JRM-1 Bu. 76823 (c/n 9267) Hawaii Mars. Delivery date: 23 April 1946. Assigned to VR-2 (Alemeda NAS). SOC 22 August 1956. Sold 1959. Converted to forest fire fighting aircraft. Registered CF-LYL (later C-FLYL) - still flying with Coulson Group at Sproat Lake, B.C.

• JRM-2 Bu. 76824 (c/n 9268) Caroline Mars. Engines changed to Pratt & Whitney R4360-4T (3,000 HP) turning 4-blade, 16.8' diameter Curtiss Electric propellers. Gross weight increased by 20,000 lbs. Delivery date: 10 May 1948. Assigned to VR-2 (Alemeda NAS). Sold: 1959. Converted to forest fighting aircraft by Forest Industry Flying Tankers. Registered CF-LYM. destroyed during Typhoon Freda at Victoria, Canada 12 October 1962.

• JRM-3 Bu 76820 - 76823 (c/n 9264 - 9267). Martin model 170b. Conversion of the remaining JRM-1's re-engined with Pratt & Whitney R3350-24WA (2,400HP) engines turning 16' 8" Curtiss-Electric props, of which the inboard two engines were fitted with reversible-pitch devices.

Civilian use

In 1959, the remaining Mars were sold for scrap. Dan McIvor, who represented a consortium of British Columbia lumber companies, recognized their potential value as water bombers and had them converted. A company called Flying Tankers Inc. was formed, and purchased the "Big Four" for aerial firefighting. The Marianas Mars crashed near Northwest Bay, British Columbia on 23 June, 1961 during firefighting operations; all four crewmembers were lost. Just over a year later, on 12 October 1962, the Caroline Mars was destroyed by Typhoon Freda while parked onshore. The Hawaii Mars and Philippine Mars had their conversions to water bombers accelerated and entered service in 1963. They appeared at local airshows, demonstrating their water-dropping ability. Flying Tankers Inc. also flew the water bombers to other hotspots around the world when a need developed, such as in August 2003, when a large forest fire threatened the city of Kelowna, British Columbia.

On 10 November 2006, TimberWest Forest Ltd. announced that they are looking for buyers of the Mars. A condition of this sale was that the purchasers would have to donate one back to Port Alberni when they are retired, as a historical attraction. The Maryland Aviation Museum and British Columbia Aviation Council have initiated a joint effort to preserve the aircraft, one in Maryland and the other at their current location in Canada. On 13 April 2007, TimberWest announced the sale of both aircraft to Coulson Forest Products, a local forestry company in Port Alberni, British Columbia. The two surviving tankers are based at Sproat Lake near Port Alberni. On 25 October 2007, the Hawaii Mars ("Redtail") arrived at Lake Elsinore in Southern California, on a private contract, to assist with the firefighting efforts containing the California wildfires of October 2007. The Philippine Mars is undergoing "extensive maintenance and renovation" and will not be ready to fly again until 2010.

Based on historical data, each plane can make a drop every fifteen minutes. Working in tandem, this equates to 7,200 US gallons (27,276 litres) every seven minutes and each drop can cover an area of up to 4 acres (1.6 hectares). The aircraft can carry up to 7,200 US gallons.

They are used to fight fires along the coast of British Columbia and sometimes in the interior.

Specifications (JRM-3 Mars)

• Crew: four (with accommodations for a second relief crew)
• Capacity: 133 troops, or 84 litter patients and 25 attendants
• Payload: 32,000 lb (15,000 kg) of cargo, including up to seven jeeps
• Length: 117 ft 3 in (35.74 m)
• Wingspan: 200 ft 0 in (60.96 m)
• Height: 38 ft 5 in (11.71 m)
• Wing area: 3,686 ft² (342.4 m²)
• Empty weight: 75,573 lb (34,279 kg)
• Loaded weight: 90,000 lb (40,820 kg)
• Max takeoff weight: 165,000 lb (74,800 kg)
• Powerplant: 4× Wright R-3350-24WA Duplex Cyclone (JRM-1 aircraft were originally powered with this engine, but modified by the Navy with more powerful Pratt & Whitney R-4360 Wasp Major "corncob" radial engines and designated JRM-3; civilian operators converted them back to Wright R-3350s) 18-cylinder radial engines, 2,500 hp (1,865 kW) each

Performance

• Maximum speed: 192 knots (221 mph, 356 km/h)
• Range: 4,300 nautical miles (5,000 mi, 8,000 km)
• Service ceiling: 14,600 ft (4,450 m)