Soviet engineers, fearing Allied shelling from cruisers, realized that they would need to strike back in a similar fashion using a submarine. Stripping out the torpedo bays allowed them to move the crew quarters and sensor systems further forward, creating a space for additional weapon systems further to the rear. Unfortunately, this was not enough room for the oversized missile launchers planned, so the engineers made a number of modifications to the original submarine's hull. Eventually, they fitted the oversized missile launchers and missiles into the submarine's mid area bay, and put the engines on small outriggers to save precious internal space. This let them use essentially the same chassis as the regular submarine.