HSTE[Omega Moderator]
4530
Breitling 817 CP-1 ...
.... were all manufactured in 1975 and issued to the Italian army. The "E.I." on the case-back stands for "Esercito Italiano". Only 500 pieces were issued and they are all individually numbered.
This one is one of the "Folgore fourty", i.e. issued to the 185th paratroopers division Folgore.
Cheers, HSTE
PS: I have actually the original metal flex bracelet (which is a hair-eater, therefore removed) and some original corresponding army paperwork