The monocoque fuselage was similarly built of 'shpon', molded birch plywood, and also had an integral fin, but it was considerably longer than that of the I-180.

It was fitted with a ducted spinner to improve cooling with the air expelled through gills as in the I-180 to provide additional thrust.

The I-185 (M-81) finally took to the air on January 11, 1941, but it was decided not to waste further development and await a more powerful engine which was fortunate as the M-81 was cancelled in May 1941.

The forward fuselage had to be redesigned to accommodate the slimmer engine and the armament was revised to three synchronized 20 mm (0.79 in) ShVAK cannon.

The flight tests of both of the latter versions were interrupted by the German invasion in June 1941 and all three prototypes, along with the entire Polikarpov design bureau, were evacuated to Novosibirsk.

All three aircraft were assigned to the 728th Fighter Aviation Regiment of the 3rd Air Army of the Kalinin Front and were tightly controlled to prevent the loss of the prototypes.

For example, all sorties had to be flown over Soviet-controlled territory and required the express permission of the 3rd Air Army staff to fly.

[6] Pilots' reports were quite enthusiastic; the 728th's commander, Captain Vasilyaka wrote: "The I-185 outclasses both Soviet and foreign aircraft in level speed.

The I-187 had a M-71F engine of 1,640 kW (2,200 hp), a bubble canopy, four 20 mm cannons, eight RS-82 rockets and an estimated maximum speed of 710 km/h (441 mph).