Offered for auction is a genuine WW2 and rare US-made Waltham Admiralty Stopwatch IN THE ORIGINAL POUCH AND BOX. These were designed for a very specific purpose in that they were calibrated to measure a distance of up to 5,000 yards over a six-second interval. This was so they could be used in conjunction with 'Asdic' sonar apparatus on board anti-submarine warships. The Asdic operator started the timer running on the emission of the sonar 'bing', the soundwave being reflected back from the submarine, so travelling twice the distance in twice the time necessary to compute the range & distance of the sub. The Stopwatch was therefore calibrated to register a speed of half that sound through the water, the scale showing approx. 830 yards per second. Comparison of of successive readings, allied to the direction-finding capabilities of of the Asdic apparatus, enabled the range, speed & course to the U-boot to be plotted. As a result depth charges could then be primed to explode at exactly the right depth to hit the submarine, In a smashing, still running condition, (though we've not been able to get the back off to inspect the workings) the facing carries the maker's name WALTHAM USA whilst the rear casing carries a large War Department Arrow etched in the metallic body in the centre with the legend PATT.6 and a serial number underneath A lovely WW-II Royal Naval anti-submarine timepiece.! Its runs - see photo's, but for some reason it doesnt always come back to 0. Can also be that I operate / press it wrongly. Great and rare 100% original item from WW2 in functional condition! See also our other interesting military books and militaria for sale!