Although described extensively in the British Museum's printed catalogue of Harleian manuscripts Harl. MS. 1413, a 16th-century manuscript containing Books VII-X of an illustrated German warfare treatise, has remained unidentified.and virtually unnoticed since the catalogue was published soon after the beginning of the 19th century. In this article the volume is re-examined and the text identified as the second part of a hitherto unknown version of the Kriegsordnung of Albrecht, 1st Duke of Prussia. The circumstances of its composition are explored and some preliminary remarks are made on its significance, not just in a military context but as a cultural artefact in its own right.