Hi-your binocs were standard issue to many departments of the navy including service on U Boats-the most common ones used on U Boats were those manufactured by Zeiss(code blc)
7x50 / 8x60 these were a far superior and tougher binocular than the Leitz(beh)-finding examples that are in good condition and not messed about is getting hard and command high prices-The 'M' means Marine-there also may be a letter 'T' this is the code for a special coating that has been applied to the lenses-the compartments inside the bino case held filters(yellow) which fitted onto the eyepieces-be careful about peeling back the rubber armour around the prism housing-it easily breaks/splits as do the eyepeice covers..be careful when cleaning the lenses as not to scratch the coatings and make sure your strap if its the original is in good condition -dropping them would be a disaster...hope info was of use......rgds Mike