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Glenn L. Martin

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Martin Models 170, 193 and 199

The Museum is working to bring the Mighty Martin Mars back to Maryland. Click here to find out more!

XPB2M-1, JRM-1 To JRM-3, Mars Flying Boats

In some respects the PBM represented an interruption in Martin's work on huge four-engine flying boats. These had become something of an obsession with the firm's founder and president. In 1938 the Navy ordered a single prototype Martin Model 170 as an experimental patrol bomber, designated XPB2M-1. This was to be the Martin Mars, a 140,000-pound behemoth that was the largest plane in the U.S. military inventory until the arrival of the B-36 intercontinental bomber in 1947. The Mars was originally conceived as a "sky battleship" or "flying Dreadnought," armed with multiple gun turrets, capable of flying long distances with huge bombloads (and Marine paratroopers as well). In speeches and articles, Glenn Martin predicted that a single Mars could capture an enemy island or "totally destroy" a rail center or shipyard. A squadron of them, he wrote, could "devastate Tokyo in one trip."

The XPB2M-1 was accordingly treated like a warship. Its keel was ceremoniously laid on August 20, 1940, with Glenn Martin driving the first rivet. Its launching into Dark Head Creek on November 5, 1941, was stern-first, after a bottle of champagne had been duly smashed over its bow. The plane's interior was laid out with separate mess rooms, berths, and washrooms for officers and enlisted men. Its commander had a private stateroom and issued his orders from a desk behind the pilots' seats. A huge bomb-bay, located in the hull underneath the wings, contained racks capable of holding five 1,000-pound bombs each. When it came time to drop them these could slide out on either side along the lower edge of the wing.

Initial taxiing tests in Middle River came to an abrupt end on the Friday before Pearl Harbor when one of the giant laminated-wood propellers threw a blade. It just missed the Martin flight engineer inside the hull and started a fire in one of the huge Wright R-3350 engines. The stricken sky battleship had to be towed closer to shore to allow firemen to put out the blaze. When the smoke cleared serious damage to the starboard wing and number-three engine nacelle were apparent. Repairs took more than six months, by which time the plane's mission had undergone a complete re-evaluation.

Pearl Harbor showed that fast carrier planes made very effective bombers indeed, while German U-boats turned the Atlantic coast into "Torpedo Alley." Thoughts naturally turned to a "sky freighter" as an alternative way to ship supplies to Britain and other battlefronts, invulnerable to torpedoes. The industrialist Henry J. Kaiser suggested that, given Martin's blueprints for the Mars, he could quickly build hundreds of the planes in his west-coast shipyards. Martin's response was ambivalent. Although the company issued calculations suggesting that building the Mars in quantity would be more cost-effective than Liberty ships, Glenn Martin was not inclined to share his prize plane with another manufacturer. Kaiser joined forces instead with Howard Hughes; this was the origin of Hughes' 400,000-pound "Spruce Goose." Like Hughes, what Martin really wanted was government support for an even larger flying boat. Plans for the 250,000-pound Model 163, projected back in 1937, were dusted off and modernized. Building five hundred six-engine Model 193's could win the war, declared Glenn Martin, and company ads frequently depicted it as a postwar airliner. Meanwhile the Navy redesignated the original Mars as a transport, XPB2M-1R, and Martin began to remove its turrets and bombing equipment.

Long before either Mars transports or the Model 193 could have been ready, the tide had turned in the Battle of the Atlantic. The Mars was sent to the Pacific instead, where it built an impressive record between 1943 and 1945, carrying cargoes of up to 34,811 pounds. Particularly impressive was the plane's ability to carry ten tons of cargo on the critical California to Hawaii route.

In January 1945 the Navy ordered twenty more Mars transports, now designated JRM-1. In comparison to the original, their hulls were to be six feet longer and the split PBM-style tail replaced by a single 44-foot vertical fin. Fewer internal bulkheads and an overhead hoist would assist cargo-handling. Maximum take-off weight grew to 148,500 pounds. Recalling the China Clippers a decade before, the first JRM-1 was christened the "Hawaii Mars" in July 1945. It crashed just two weeks later in a landing accident on Chesapeake Bay. Four more JRM-1's were completed in 1945, but, in the wake of V-J Day, the Navy order was cut to six.

Peace allowed Martin pursue the long-cherished goal of selling giant airliners. The Mars was offered in several commercial versions for passengers and cargo. Re-engined with massive four-row Pratt and Whitney R-4360 Wasp Majors, the largest piston engines made, Model 170-21A offered transatlantic range with 58 sleeper or 79 coach seats. Model 170-24A could seat 105 for shorter ranges. But the construction of so many long runways during the war eliminated one of the flying boat's principal advantages. Martin recognized this and began work on a 145,000-pound landplane using the same engines and wings as the JRM-1; the Model 199 was to have a floor level no higher than that of a truck. Other four-engine airliners were already on the scene, however. There were no airline purchasers for either the 170 or the 199.

The Navy did purchase its sixth and last Mars with Wasp Major engines, which enabled the single JRM-2 to carry an extra 18,000 pounds of cargo on the San Francisco-to-Hawaii run. The four earlier planes were eventually re-engined with Wasp Majors as well and designated JRM-3's. All five served in the Pacific, carrying military personnel, Korean-war wounded, blood plasma, and other priority cargo over the same routes as were once flown by the glamorous clippers. Like them, they were duly christened for Pacific destinations: Philippine, Marianas, Marshall, a second Hawaii, and Caroline.

A fire destroyed the Marshall Mars in 1950; the other four JRM's served the Navy until 1956. They were then sold as surplus to Forest Industries Flying Tankers Limited, a Canadian firm, which uses them to drop 60,000-pound loads of water and foam on forest fires. The Marianas Mars crashed in an accident in 1961, and the Caroline Mars was destroyed in a hurricane a year later - but as they approached age 40 both the Philippine and Hawaii Mars were still flying.




© 2006 The Glenn L. Martin Maryland Aviation Museum
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