A WWII Kriegsmarine Zeiss 13.5cm f4 Sonnar Lens, Contax Fit. From German U-Boat 1021. Serial #2611299, signs of normal+ use. Steel body with MF1021 engraving. During WWII the German navy (Kriegsmarine) issued a Contax outfit to each of their submarines, with the camera and lens(es) marked MF, followed by the U-boat number. MF was thought to stand for Marine Flieger (Naval Air Arm of the Germany Navy). For details of U-Boat 1021 see https://en.wikipedia.org/wiki/German_submarine_U-1021