Naval Aircraft Factory (NAF) PN-12
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.