In March 1925, the US Navy ordered nine P-1s with provision
for float operation as F6Cs (the F5C designation
was not assigned, to avoid confusion with the F-5 flying
boat), five of these being delivered as F6C-1s and four
(with arrester hooks) as F6C-2s. These had similar
power plant and armament to the USAAC's P-1. Two of
the F6C-1s were later converted to -2 standard. In 1927,
35 additional aircraft were ordered, these using the
P-1A airframe and being designated F6C-3. Two F6C-1s
were converted to -3 standard and one F6C-3 was fitted
with a Pratt & Whitney R-1340 radial as the XF6C-3.
The US Navy had decided, by 1927, to standardise on
air-cooled radial engines, which were more easily
maintained at sea than liquid-cooled inline engines.
Accordingly, after trials with a Pratt & Whitney R-1340-
engined F6C-3, a production contract was placed for 31
fighters powered by this 410hp radial as F6C-4s. The
first of these aircraft, which was retained for test purposes,
was assigned the designation XF6C-4 and deliveries
commenced in February 1927. Possessing the
same twin-gun armament as its predecessors, the
F6C-4 proved more manoeuvrable than the V-1150-
powered models, but was becoming obsolescent by the
time that it was delivered. It remained first-line equipment
only until the beginning of 1930. Experimental
F6C models were the XF6C-5 (first F6C-1 fitted with a
525hp Pratt & Whitney R-1690 Hornet), XF6C-6 (an
F6C-3 converted to parasol monoplane configuration
for the 1930 Thompson Trophy race), F6C-6 (an F6C-3
modified for 1929 air races and returned to -3 standard),
and the XF6C-7 (an F6C-4 with an inverted air-cooled
Ranger SGV-770 engine).
