In D-Day, Stephen Ambrose describes extensively the preparations for Operation Overlord.  My favorite passage so far (from page 153) describes preparations taken within assembly areas (called “sausages” — read the book if you need to know why) immediately before the invasion:

Condoms were issued, by the millions.  Some were blown up into balloons or filled with water and tossed around, but most were put to more practical, if unintended, use.  The infantrymen put them over the muzzles of their M-1 rifles; the rubbers would keep out sand and water and would not have to be removed before the weapons were fired.  Hundreds of men put their watches in condoms and tied them off; unfortunately, the condoms were not large enough to hold wallets.