Historic Aircraft: The New Flying Boats

By Norman Polmar

The next two aircraft-designated PN-8-had two Packard 475-hp water-cooled V-12 engines and a metal hull. The subsequent PN-9 (converted from one of the PN-8s) and two newly built PN-10 aircraft were similar. The engines had problems-the Navy always preferred simpler, air-cooled engines-and radial engines were thus used to produce the later PN-12.

The PN-9, however, was a good performer. On 1-2 May 1925, Navy Lieutenants Clarence H. Schildhauer and James R. Kyle, on a test flight over Philadelphia, broke the world endurance record for Class C seaplanes by remaining aloft for 28 hours, 35 minutes, 27 seconds.

The following 1 September, the PN-9 took off from San Francisco for Pearl Harbor. With Commander John Rodgers-Naval Aviator No. 2-in command and navigating, and a crew of four, the aircraft was heavily laden with 1,278 gallons of fuel in its tanks and another 50 gallons in five-gallon cans. The plane nevertheless ran out of fuel and came down several hundred miles short of its destination. Despite an extensive air search, the PN-9 was lost at sea for ten days. Rodgers and his crew, meanwhile, improvised. Relying on their training as sailors, they fashioned a sail out of the lower wing's fabric and set out for Kauai Island. After covering about 450 miles they were sighted on 10 September by the submarine R-4 (SS-81) about ten miles short of their goal. Still, the aircraft had flown 1,841 statue miles, a record for Class C seaplanes that stood for almost five years.

Four PN-11 variants were built, with two engines being evaluated in the aircraft. The hull lines of the PN-11s marked the first major departure from the F-5-L design, featuring a wider hull that eliminated the sponsons, a feature of the older hull. The first aircraft was also fitted with twin vertical tail surfaces. (The last three aircraft were later designated XP4N.)

The two follow-on PN-12s represented the definitive design. Like its predecessors in the PN-series, the PN-12 was a biplane designed specifically for the patrol/antisubmarine role. Single .30-caliber machine guns were fitted in the bow and amidships, and four 230-pound bombs could be carried under the lower wing. Equally powered by twin 525-hp engines, one PN-12 had twin Pratt and Whitney Hornet R-1850s, and the other Wright Cyclone R-1750s. They gave the aircraft a top speed of 114 mph and a range at cruising speed of just over 1,300 miles. It was flown by a crew of five (in open cockpits), and a relief crew could be carried for long patrols. On 3-5 May 1928, the Cyclone-powered PN-12 set another world seaplane record, covering a distance of 1,243 statue miles in 17 hours, 55 minutes.

The Naval Aircraft Factory was not capable of large-scale production, and the Navy decided to have the PN-12 manufactured by private aircraft companies. The Douglas Aircraft Company produced 25 PD-1 aircraft and the Martin Company built 30 PM-1 variants based on the NAF design. Subsequently, Martin built 25 PM-2 variants and the Keystone Aircraft Corporation built 18 similar PK-1 aircraft, the latter being twin-rudder versions. Thus, the PN-12 gave birth to 98 offspring. These aircraft served in the Fleet until 1938.

In 1927 the Hall Aluminum Aircraft Company developed another PN derivative, the XPH-1. 2 This was the first U.S. Navy flying boat to have all-metal stressed skin construction, which provided a considerable savings in weight. In the event, only ten PH-1s were built as the Navy moved to more advanced flying boat designs. But the Coast Guard procured seven improved Hall PH-2s and seven PH-3s for air-sea rescue missions. Some of these aircraft served into World War II.

Thus, the same basic flying boat design-from the F-5-L to the PH-3-spanned two world wars, a most notable achievement.


1. See CAPT M. J. Stack, USN, "Patrol Planes to the Orion and Beyond," Naval Review 1966 (Annapolis, MD: U.S, Naval Institute, 1965), pp. 58-77; and Gordon Swanborough and Peter M. Bowers, United States Navy Aircraft since 1911 (Annapolis, MD: Naval institute Press, 1968), pp. 334-337.

The designation F-5-L was derived from the British F.5, with the letter "L" indicating use of the American-built Liberty engine; PN-5 indicated Patrol aircraft, Naval Aircraft Factory, the fifth design.

2. See Swanborough and Bowers, United States Navy Aircraft, pp. 254-255.


Norman Polmar is an analyst, author, and consultant, specializing in naval, aviation, and technology subjects.  He has directed studies related to the Soviet/Russian navies for various government organizations, and has been a consultant or advisor on related issues to three U.S. Senators,  the Speaker of the House, the Deputy Counselor to the President, and three Secretaries of the Navy. He has visited the Soviet Union/Russia several times as a guest of the  Navy commander-in-chief, the submarine design bureaus, and the Institute of U.S. Studies. 

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