The chief long-range patrol flying boats of the United States Navy at the end of World War I were the Curtiss H.16 and the similar Felixstowe F5L. The F5L was a license-built version of the British Felixstowe F.5 using the AmericanLiberty engine. The series of Felixstowe flying boats, developed by the Seaplane Experimental Station, had started with improving the hull of the Curtiss H12. The Naval Aircraft Factory, which had built F.5Ls during World War I, continued development of the design, which was redesignated PN-5 in 1922, with the final two being built to an improved design, the F-6L. In 1925, the Naval Aircraft Factory produced a version with new wings with an airfoil section of greater maximum lift coefficient. It was powered by experimental Wright T-2 piston engines, and was designated PN-7. Although the new wing proved successful, the engines were unreliable, and the wooden hull inherited from the F.5 required much maintenance, so two aircraft with metal hull construction, powered by Packard engines, were built as the PN-8. Further, similar aircraft were built as the PN-9 and PN-10, but the water-cooled V-12 Packard engines were disappointing and radial engines were substituted to produce the PN-12. This combination of the revised wings introduced by the PN-7, with a metal hull and radial engines met the requirements of the Navy and therefore the PN-12 formed the basis of more extensive production to re-equip its patrol squadrons. As the production capacity of the Naval Aircraft Factory was limited, production was contracted out to several aircraft companies, with versions being built by Douglas, Keystone Aircraft and Martin. The PN-12 was a twin-engined biplane with fabric-covered metal-framed wings, its engines being mounted in nacelles between the wings. While the hull was constructed of metal, it was otherwise similar to that of the F.5L, with the large sponsons that were a feature of both that aircraft and the Felixstowe and Curtiss flying boats to which it could trace its heritage. It had a standard crew of five, but was capable of carrying a relief crew for long patrols. The PN-11 featured a revised hull which eliminated the sponsons. It also used twin vertical tails. Four of this variant were built. They were the basis of the Hall PH flying boats, some of which remained in service until World War II.
Operational history
The early prototypes of PN sea planes were used in a series of long-distance flights. During the afternoon of 31 August 1925, an attempt was made to fly a pair of PN-9 planes non-stop from San Francisco to Hawaii, a distance of nearly 2,400 miles — a trip anticipated to take 26 hours to complete. The first plane to start was forced to land 300 miles outside of San Francisco due to a failure of oil pressure, with the crew rescued by the destroyer USS William Jones and the aircraft towed back to port. The second PN-9 to depart, captained by U.S. Navy Commander John Rodgers, flew 1,841 miles before running out of fuel when anticipated tailwinds that would have slowed gasoline consumption did not materialize. The plane was unable to make contact with the naval airplane tender USS Aroostook, a ship stationed along the PN-9's flight path and was forced to land at sea when both engines stopped functioning. With power lost, the plane was unable to send or receive radio signals. Although this was at the time a new distance record for seaplanes, the plane remained hundreds of miles short of the nearest landfall and the situation of the crew, with limited quantities of food and water, appeared dire. Since seas were moderate, the decision was made to attempt to sail the plane to Hawaii. The crew then rigged crude sails made from fabric torn from the aircraft's wings and sailed the aircraft a further 450 miles, finally being spotted on the ninth day about 15 miles off the southeast coast of the Hawaiian island of Kauai. In the aftermath of the headline-grabbing rescue, Commander Rogers was promoted to the position of Assistant Chief of the Navy's Bureau of Aeronautics. PN-9 No. 1, the same plane sailed to Hawaii, did not fare as well, later ditching in the Caribbean Sea during an attempted long distance flight to South America and subsequently sunk as a navigation hazard. The two PN-12s were also used to set various records, including range and speed over circuit records. The various production derivatives of the PN-12 entered service with the US Navy from 30 April 1928, when VP-7D received its first Douglas PD-1, remaining in service until July 1938, when the last Keystone PK-1 was retired. Three Martin PM-1s were also supplied to the Brazilian Navy in 1930, and used in bombing raids during the 1932 revolution.
