1x40 M44 U-boat Flak gun sight 'dow'

A very rare original late-war 1x40 M44 sight for the U-boat deck-mounted AA Flak gun. 
 
Produced by Optikotechna under the 'dow' maker code, during 1944, this optic was designed to be both water and airtight like the UDF binocular - enabling it to be left fitted to the submarine, externally, during any emergency dive manoeuvres. 
 
It still retains the vast majority of the original ship grey outer paint finish; as well as the adjustable headrest pad, rubber eyepiece, swivel-mounted objective lens cover and even the quick-aim iron sights!
 
The sight is still very much usable, producing a good image - with the internal anti-aircraft aiming reticule remaining intact and clearly visible inside. 
 
A really interesting and complete example of one of the more rarely encountered optics, which would make a great addition to any KM / U-Boat related collection!