The Martin JRM Mars is a retired large, four-engined cargo transport flying boat designed and built by the Martin Company for the United States Navy (US Navy). It was the largest Allied flying boat to enter production during World War II, although only seven flying boats were completed.
The Mars was developed during the late 1930s and early 1940s as a scaled up derivative of the PBM Mariner patrol bomber, internally designated Model 170. Under contract from the US Navy, an initial prototype, the XPB2M-1 Mars, performed its maiden flight on 23 June 1942. While originally intended to be adopted as a long-range ocean patrol flying boat, as the conflict progressed, the Mars was reoriented towards the long-range transport mission, thus redesignated XPB2M-1R. The flying boat commenced ferrying cargo to Hawaii and the Pacific Islands on 23 January 1944. While a batch of 20 Mars was at one point on order for the US Navy, the service opted to curtail the order to seven aircraft following the end of end of World War II. An envisioned civil airliner variant, Model 170-24A, was never put into production.
Up until 1956, the US Navy typically used the type on San Francisco-Honolulu route, after which it was withdrawn from service and stored. Thereafter, four of the surviving Mars were converted for civilian use as firefighting water bombers. Two of the aircraft were based at Sproat Lake, just outside of Port Alberni, British Columbia, Canada, one of which, Hawaii Mars, remained in operation until 2016, after which it was preserved at the British Columbia Aviation Museum. The Philippine Mars is also to be permanently displayed at the Pima Air & Space Museum in Tucson, Arizona. No remaining examples are operational.
Design and development During the late 1930s, the Glenn L. Martin Company was engaged in the production of the PBM Mariner patrol bomber for the United States Navy (US Navy). From an early stage of the Mariner's development, the company's design staff had started work on the Model 170, a considerably larger four-engined derivative. In August 1938, following a presentation of the Model 170 to the Bureau of Aeronautics, the US Navy placed an order for one prototype, designated XPB2M-1 Mars. Due to other work commitments, the company was unable to start construction of this prototype until mid-1940. In early November 1941, the XPB2M-1 was ready to conduct taxiing tests; at the time, it was the largest flying boat as well as the third largest aircraft of any type then in existence in the world.
The XPB2M-1 shared its general hull configuration and its twin-fin arrangement with the preceding Mariner. It was powered by four Wright R-3350 Duplex-Cyclone 18-cylinder radial engines, each one rated to produce 2,200 hp. The type's envisioned armament arrangement consisted of two bomb bays, one under each wing, that could accommodate up to five 1,000-pound bombs, while a total of five turrets, each armed with a single .30-caliber machine gun, were present for self-defense.
The flight controls of the Mars have been described as being strenuous to operate, the rudder being one of the few controls to be boosted. Accordingly, the pilot and flight engineer had to cooperate closely when operating the flying boat both in flight and while upon the water. Flights, which were limited to day time, typically required considerable attention to trimming. To provide greater control to manoeuvre while alighting, reversible propellers were fitted to two of the engines; this function was guarded by a safety switch under the control of the flight engineer. While landing, full flaps were typically deployed. Engine run-ups while aligning were performed with considerable attention being paid to keeping the nose of the flying boat up. The external inspections performed both pre-flight and post-flight were performed using a boat.
Ground testing was protracted on account of an engine fire that inflicted substantial damage to the prototype's starboard wing, necessitating six months of repair work. the XPB2M-1 conducted its maiden flight on 23 June 1942. While the flight test programme proceeded, wider events impacted the programme. By this time, the original patrol bomber concept the flying boat was intended to fulfil was considered obsolete, US Navy planners having redirected their focus for combat aircraft being based onboard their aircraft carriers instead. Instead, it was decided that the aircraft could be used to address the ongoing threat posed to Atlantic shipping by the U-boats of Nazi Germany. Accordingly, the Mars was stripped of all armament and bombing apparatus for conversion into a transport aircraft, designated as the XPB2M-1R.
In 1943, the industrialist Henry J. Kaiser offered to license-build the Mars in quantity at multiple shipyards on the West Coast, however, Glenn Martin were uninterested in sharing the production rights with another manufacturer, thus nothing came of this proposal. Factory testing of the transport conversion was completed in mid-1943, after which the XPB2M-1R was delivered to the US Navy for operational evaluation and crew training. In June 1944, having been sufficiently satisfied by the performance of the prototype, the US Navy ordered 20 of the modified JRM-1 Mars. These production aircraft differed somewhat from the earlier prototype, including the use of a single vertical fin, the hull being lengthened by three feet, fewer internal bulkheads, and the adoption of a new cargo-handling system.
The first, named Hawaii Mars, was delivered in late July 1945, but was lost in an accident on the Chesapeake Bay only weeks after its first flight. However, shortly after the end of World War II, the US Navy opted to scale back their order, purchasing only the five aircraft which were then on the production line.Bridgman 1946, pp. 244–245. Accordingly, the other five Mars were completed, the last of which was delivered in 1947. The company had worked on an airliner version of the Mars, the Model 170-24A, capable of seating up to 79 passengers and to be powered by Pratt & Whitney R-4360 engines, the postwar market for civilian flying boats was relatively meagre, leading to the concept being discontinued.
Operational history
U.S. Navy service
Named the Marianas Mars, Philippine Mars, Marshall Mars, Caroline Mars, and a second Hawaii Mars, the five production Mars aircraft entered service ferrying cargo to Hawaii and the Pacific Islands on 23 January 1944.Associated Press, "Aerial Box Car Sent To Nimitz", The Spokesman- Review, Spokane, Washington, Monday 24 January 1944, Volume 61, Number 255, page 1. The last production airplane (the Caroline Mars) was designated JRM-2, powered by Pratt & Whitney R-4360 engines, and featured a higher maximum weight and other improvements. On 4 March 1949, the Caroline Mars set a new world passenger load record by carrying 269 people from San Diego to San Francisco, California.Boyne 2007, p. 465. 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 U.S. Navy cargo on the San Francisco-Honolulu route efficiently.
However, in 1956, the Us Navy decided to end its use of flying boats for transporting cargo, leading to the final military flight of the type taking place on 22 August 1956. Thereafter, the remaining flying boats were beached at Naval Air Station Alameda for a time.Goebel, Greg. Air Vectors, 6 May 2006. Retrieved: 13 November 2010.
Civilian use
In 1959, the remaining four Mars flying boats were to be sold for scrap. However, a Canadian company, Forest Industries Flying Tankers (FIFT), was formed and bid for the Mars as well as the sizable inventory of spares for the type. The company, which represented a consortium of British Columbia forest companies, was successful, the sale being completed in December 1959. The four aircraft were flown to Fairey Aviation at Victoria, British Columbia, for conversion into water bombers. This conversion process involved the installation of a plywood tank in the cargo bay with retractable pick-up scoops to allow uploading of water while taxiing – could be taken on board in 22 seconds. Other changes included the removal of surplus military apparatus and the installation of overhauled R-3350-24WA engines. Later on, some of the hull fuel tanks were replaced with water tanks.
The Marianas Mars crashed near Northwest Bay, British Columbia, on 23 June 1961 during firefighting operations; all four crew members died. Just over a year later, on 12 October 1962 while parked onshore at the Victoria airport, the Caroline Mars was damaged beyond repair by Typhoon Freda when it was blown , breaking its back. The Hawaii Mars and Philippine Mars had their conversion into water bombers advanced and entered service in 1963. They appeared at local airshows, demonstrating their water-dropping ability. Flying Tankers Inc. flew the water bombers to hot spots around the province when a need developed, such as in August 2003, when a large forest fire threatened the outskirts of Kelowna, British Columbia.
On 10 November 2006, TimberWest Forest Ltd. announced they were looking for buyers of the Mars. A condition of sale was that the purchaser would have to donate one plane back to Port Alberni when they were retired, as a historic attraction."TimberWest Seeks Buyers For Martin Mars Water Bombers." TimberWest Forest Ltd., 12 November 2006. The Glenn L. Martin Maryland Aviation Museum and British Columbia Aviation Council initiated a joint effort to preserve the aircraft, one for display in Maryland and the other at the current location in Canada. Maryland Aviation Museum, 12 November 2006. 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 were operated by Coulson Flying Tankers from their base at Sproat Lake near Port Alberni until their retirement in 2024. On 25 October 2007, the Hawaii Mars ("Redtail") arrived at Lake Elsinore in southern California, on a private contract, to assist with firefighting efforts at the California wildfires of October 2007. Meanwhile, the Philippine Mars had been undergoing "extensive maintenance and renovation" and was expected to be ready to fly again by 2010. , the Hawaii Mars was in service fighting the La Brea Fire east of Santa Maria in Southern California.
The aircraft can carry of water and each deployment can cover an area of up to 4 acres (1.6 hectares). The aircraft can also carry up to of foam concentrate for gelling the load drop. They had been mainly used to fight fires along the coast of British Columbia and sometimes in the interior. By July 2010, the Martin Mars was being used to fight the Mason Lake/Bonaparte Lake fire north of Kamloops.
On 23 August 2012, the Coulson Group announced that the Philippine Mars, due to its lack of use for five years, would be retired and flown to the National Naval Aviation Museum at Naval Air Station Pensacola, Florida, to become a static exhibit. The aircraft was repainted to its original U.S. Navy colors and was to have been delivered to the museum in November 2012. After many delays, the trade deal of transferring the aircraft to the museum was put on hold by the Navy in June 2016, pending the outcome of the 2016 US Presidential election.