C.O.S.D = Combined Operations Stores Dept. Not sure if it applies to these knives but it did apply to some other 'sensitive' equipment. One that I can think of that isn'r sensitive any more was the old SS20 night sight (and others) that fitted to the Sterling L2A3 and the L34 guns. Those had a COSD prefix and even if you had the part number and submitted a demand for one. All you'd get back was a snott-o-gram asking why.....