(Helmtauchermesser). A rare and exceptionally well-preserved Austro-Hungarian Navy deep sea diver’s knife, measuring 34.5 cm in total length when fitted with its scabbard. It features a 21 cm-long magnetic steel blade with a blunted tip and sharpened lower edge. Stamped onto the reverse ricasso is a maker’s mark of “WKC” for Weyersberg, Kirschbaum & Cie, Solingen, topped by the firm’s classic knight’s helmet logo. The obverse ricasso bears a further distributor’s mark of “AUG. LÜNEBURG, KIEL”. The blade sits securely within a circular base with a threaded outer circumference to accommodate the scabbard, with a fully-intact black rubber buffer pad forming a tight seal when the scabbard is fixed in place. The handle consists of a single piece of solid brass which features cascading ribbed design to allow for a secure grip. Stamped onto the crossguard are an Austrian imperial eagle and Crown of St. Stephen, representing the Dual Monarchy of Austria and Hungary, respectively. Completing the dagger is a finely-engraved Austro-Hungarian imperial crown. It is accompanied by its matching scabbard, constructed of a circular brass tube. Carefully engraved onto the side of the tube is an inscription of “MBLT. WEBER / U-BOOT-STATION POLA”, circumscribing the monogram of the Austro-Hungarian Navy’s U-Boat pen at Pola (now Pula, Croatia). The throat retains a threaded interior, meeting the analogous threading emanating from the knife’s crossguard for secure closure. An integral loop emanates from the side of the throat for the accommodation of a strap. Both the blade and brass features demonstrate a consistent patina, which complements the knife’s aged appearance. Free of any evident wear or damage, this rare and personalized deep sea diver’s knife is in an overall extremely fine condition.