It was anticipated that the main source of damage to such an aircraft would be small arms fire from the ground, meaning that the plane had to be well-armored around its cockpit and engines. Similar protection was also needed in the canopy, in the form of 75 mm (2.95 in) thick armored glass. The aircraft was expected to be attacking in low-level, head-on strafing runs, so the cockpit had to be located as close as possible to the nose, in order to maximize the visibility of its targets. Another, non-operational, requirement severely hampered the designs: the RLM insisted that the new design be powered by engines that were not being used in existing aircraft, so that the type would not interfere with the production of established types deemed essential to the war effort.