The PN flying boats were twin-engine
biplanes with their engines mounted in nacelles between the fabric-covered wings. Other than on the PN-11 which had a different hull form, the hull had large chines running back to the first step similar to those on the F.5L. It had a standard crew of five, but was capable of carrying a relief crew for long patrols. Some F.5L/PN-5s were later upgraded to PN-6 standard. Neither the PN-5 or the PN-6 designation was used outside of official paperwork, and these aircraft were simply referred to as F.5Ls. The
PN-7 was a 1925 development with an improved thicker section, shorter-span wings with a more modern
airfoil section, and were powered by two experimental
Wright T-2 V-12 engines. Two were built. The
PN-8 was developed due to problems with the wooden hull, which quickly absorbed hundreds of pounds of water and was maintenance intensive, so two aircraft with a metal hull of the same shape as the F.5Ls, and fitted with the new wing, were built. Due to reliability problems with the Wright T-2, they were powered by two V-12
Packard 1A-2500 engines. 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 as the
PD-1, by
Keystone as the
PK-1 and by
Martin as the
PM-1 and
PM-2. These each had their own differences from the PN-12, as the Keystone PK-1 and Martin PM-2 the twin fins and rudders of the PN-11, while the PM-1 and PM-2 also had an enclosed cockpit, and the PK-1 had a modified hull form with a sharper bow. These also formed the basis for the
Hall PH flying boats, with a different hull fitted with an enclosed cockpit, and some of these remained in service until
World War II. ==Operational history==