Great security story from an obituary of former OSS agent Roger Hall:

One of his favorite OSS stories involved a colleague sent to occupied France to destroy a seemingly impenetrable German tank at a key crossroads. The French resistance found that grenades were no use.

The OSS man, fluent in German and dressed like a French peasant, walked up to the tank and yelled, "Mail!"

The lid opened, and in went two grenades.

Hall's book about his OSS days, You're Stepping on My Cloak and Dagger, is a must read.

Source: Schneier on Security