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.