There seems to be a lot of misinformation in this thread. The Cyclone powered Hawks are a confusing bunch, yes. First off, the F11C. This went into production as the F11C-2. This was a fixed gear, R-1820 powered fighter for the Navy. During flight test, it was found that the aircraft performed better as a dive bomber than it did a fighter. The Navy reclassified it as a "bomber-fighter" in early 1934, redesignating it as the BFC-2. About the same time as the redesignation, a retrofit kit was supplied, and the aircraft received a raised turtledeck and "semi-cabin" canopy. The export variant of the F11C came in two flavors, the Model 35 and Model 65. These could be fitted with landing gear or floats. Export versions went to Bolivia, Colombia, Peru, Turkiye, Cuba, Siam, China and Ernst Udet.
While bearing a resemblance to the F11C-2/BFC-2, the Navy's BF2C was significantly different from the earlier fixed gear Hawk. The prototype of course, was the fifth F11C-2 off the production line. It was redesignated as the XF11C-3, but eventually became the XBF2C-1. The production BF2C-1 was purchased by the Navy and equipped only one Squadron, VB-5B. They were withdrawn from service after one year due to vibration issues rooted in the natural frequencies of the engine and the aluminum wing structure. During testing, when carrying a bomb or aux tank, the aircraft vibration caused fatigue issues that eventually caused the aircraft to be withdrawn. One fix was to install a "ring vane" when carrying a ventral external load. This helped, but not enough.
The BF2C-1 was exported as the Model 68/Hawk III. Hawk IIIs were purchased by China, Thailand and Argentina plus a Turkish demonstrator. There was a single Model 79/Hawk IV with a fully enclosed canopy. This was acquired by Argentina and was destroyed on 10/26/37 when the bomb it was carrying detonated in flight.
Rich