By the time the XPB2M-1R was delivered to the Navy, the tide of war had turned in favor of the Allies on both ocean fronts.

Glenn L. Martin was said to have been obsessed with big flying boats. His obsession would see its ultimate expression in the Martin Mars, among the largest aircraft ever built. Remarkably, two of these water-based behemoths, once destined for the scrap heap, remain in service today as firefighters, more than six decades after they first flew.

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Although Martin’s role as a U.S. Navy contractor dated to 1916, his interest in flying boats actually came years later, when the Naval Bureau of Aeronautics (BuAer) contracted with his firm in mid-1929 to manufacture 25 PM-1s. The PM-1 was a twin-engine biplane flying boat built according to detailed plans and specifications issued by the government-owned Naval Aircraft Factory (NAF). Martin’s order was part of a larger effort by the Navy during the late 1920s to replace its obsolescent fleet of World War I–era flying boats with newer designs. Similar contracts were awarded to other aircraft manufacturers. Five more PM-1s were added to Martin’s contract in 1930, and in 1931 the Navy ordered 28 improved PM-2s.

While construction of the PM series was ongoing, BuAer assigned Martin an even more advanced flying boat project, a three-engine monoplane designated the XP2M-1. Interestingly, the design’s basic blueprint had been conceived by Con­solidated Aircraft and tested in early 1929 as the XPY-1. This was a byproduct of standard naval procurement methods of the 1920s, whereby rights to a particular aircraft design became the property of the Navy and could ultimately be produced by any of its airframe contractors, including NAF.

In 1931, once the XP2M-1 had been evaluated, BuAer directed Martin to reconfigure the design for two engines as the XP2M-2. This was ordered into limited production in 1931-32 as the P3M, with three delivered as the P3M-1 and six as the P3M-2. The P3Ms operated alongside Consolidated’s analogous P2Y production series, marking the beginning of a heated rivalry between Martin and Consolidated over various flying boat contracts during the 1930s.

Having established itself as a seaplane builder of some repute, Martin received a request in 1931 from Pan American Airways to design a long-range, passenger-carrying flying boat capable of operating on transoceanic routes in the Atlantic. But in 1933, before any final design had been fixed, Pan American changed its requirements to capability for routes in the Pacific. The route, as finally determined, entailed an 8,200-mile flight from San Francisco to Manila, in the Philippines, via Hawaii, Midway, Wake and Guam. It was later extended to include Hong Kong. At a minimum, this required an airplane capable of carrying fuel, passengers and mail over the 2,410-mile segment between California and Hawaii, a highly ambitious undertaking for any aircraft manufacturer of that era.

When it flew in December 1934, the Martin Model 130, dubbed China Clipper by Pan Am, represented state-of-the-art flying boat design. A combination of advanced aerodynamics and four 850-hp Pratt & Whitney R-1830 double-row radial engines enabled it to lift more than twice its empty weight, thereby exceeding the payload ratios of contemporary landplanes such as the Boeing 247 and Douglas DC-2/-3. Two more Model 130s were delivered to Pan Am in 1935-36. In its contest against Boeing’s new Model 314, however, Martin’s efforts to sell the 20-percent-larger Model 156 were unsuccessful, and the sole example was sold to the Soviet Union in 1938.

Starting in 1933, Consolidated’s PBY series dominated the Navy’s flying boat market, as illustrated by the sale of 100 PBY-1s and -2s between 1935 and 1937 (a truly enormous quantity by Depression-era standards). Consolidated also attempted to interest BuAer in its much larger four-engine XPB2Y-1. Martin, after successfully selling large numbers of B-10 bombers to the Army, endeavored to regain a share of the naval flying boat market in 1936 by submitting a competitive proposal for the four-engine Model 160. But BuAer promptly rejected it, citing a preference on the basis of cost for twin-engine patrol boats. Apparently undeterred, Martin submitted a second proposal in early 1937 for the twin-engine Model 162, which the company claimed would be 20 percent faster than the PBY and possess twice its range and payload. When Consolidated disputed Martin’s claims and threatened the Navy with legal action, Martin quickly responded by building a three-eighths scale proof-of-concept demonstrator, the Model 162A “Tadpole Clipper,” which confirmed the company’s performance projections during tests in November 1937. By the end of the year, Martin had received an order to build 21 Model 162s as the PBM-1 Mariner. The company would manufacture a total of 1,366 PBM-1, -3 and -5 aircraft over the next 12 years.

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