Panzer IV front hull, two periscope holes were drilled above the Fahrersehklappe 50 (driver flap 50mm armor) or Driver's Armor Visor to avoid direct line-of-fire if flap was opened. Crewmen's headphone wires came from electrical wires painted TESTOR Military Brown.

Rollover : Prismenspiegelkuppel (Prism Mirror Dome or Commander's Copula) enabled commander to recon the battlefield from inside the tank via armored window slits. Surprisingly, although Soviets were innovative tank designers (ex. T-34, T-34/85, IS-2 tanks), they did not install tank copulas until the late war years and relied instead on fixed periscope mounts.

Panzer IV hull was divided into driver shaft - fighting compartment - engine sections, made from austenitic and chromium-molylodenum steel via electric furnace process. Tank parts were welded together compared traditional riveted construction of 1930s era, but during combat riveted tanks would split their seams upon shell impact, ricocheting rivet fragments into tank's interior.

With reputable engineering companies throughout Germany, such as Rheinmetall-Borsig, Daimler-Benz, MAN, Henschel, Krupp, Heereswaffenamt worked was divided among these firms. For example, Rheinmetall designed the tank shell ballistics with a tungsten carbide sabot round called Triebspiegelgeschoss HK (Impulse Mirror Projectile HK), while Krupp concentrated on gun design. Sabot - en.wikipedia.org/wiki/Sabot