The change in position of the guns and the extension of the air intakes, which looked "uncannily like a double-barreled shotgun," allowed the nosewheel to be moved forward to lengthen the wheelbase. The guns were mounted behind the nosewheel well and a special shield was added to protect the gun barrels from debris thrown up by the nosewheel; it was mechanically linked to the nosewheel and extended when it did. Other changes included the replacement of the original AM-5F engines by the Tumansky RD-9V, an improved version of the AM-5F, the normal bombload was increased to 1,000 kg and in overloaded condition, and a rearview mirror was added to allow the pilot to better observe the rear upper hemisphere.