One of these aircraft (serial number 04-11) was fitted with an armored backrest plate over the rear position, self-sealing fuel tanks which filled with inert gas as they emptied, three "RO" rocket launchers under each wing for as many RS-82 rockets, an axial motornaya pushka-mount 20 mm ShVAK cannon firing through the propeller spinner, with 120 rounds, and two 7.62 mm ShKAS machine guns under the cowling, each with 750 rounds.