Each Il-4 improvement multiplied the redesign burden

The Il-4 redesign began with genuine combat needs, especially protecting gunners whom fighters deliberately targeted. Armour added weight, which demanded more powerful engines and then a stronger airframe able to carry the new loads. Additional crew positions and firepower multiplied that cycle instead of solving one isolated weakness. A clean three- or four-engine design might have offered a better power-to-weight solution. The twin-engine route remained attractive because it was quicker to build and could continue through similar production arrangements, although that industrial convenience locked the programme into mounting compromises.