Complex sentence: One of his most talented designers, Rodolphe Ernst-Metzmaier, produced the final drawings which included a fully rotating turret, a feature already existing on several military armored cars of that period (e.g. Rolls-Royce).
Split into simpler sentences: One of his most talented designers, Rodolphe Ernst-Metzmaier, produced the final drawings. It included a fully rotating turret, a feature that had already been successfully applied to military armored cars of that period (e.g. Rolls-Royce).