Operation Mincemeat [http://en.wikipedia.org/wiki/Operation_Mincemeat]- a WW2 operation of deception.
The short version; British troops took a dead bum, dressed him in officer uniform and dumped his corpse outside of spain with a briefcase carrying plans to invade Greece and Sardinia instead of the more likely target Sicily. When Hitler moved all his troops to Greece, The Allies waltzed into Sicily unhindered. The British picked up a habit of fooling the Germans with stupid shit like this, and prior to D-day they convinced the Germans they were going to invade Calais, by creating a fuckton of inflatable tanks and leaving them in plain sight around Dover.
From the Cold War, an oddly Fallout-esque weapon- the Davy Crockett [http://en.wikipedia.org/wiki/Davy_Crockett_%28nuclear_device%29]. It was a recoilless rifle with a small nuclear warhead stuck on the end, intended to allow infantry to nuke oncoming enemy troops