Sam Browne, minus left arm
General of the Armies, John J. Pershing in France, October 1918 wearing the Sam Browne belt.
I'm not sure where to find one or even where to look (minus ebay, but the ones I saw there were pretty expensive/authentic looking), but I want what I have come to find is called a "Sam Browne Belt" - named after a British army officer who served in India during the 19th century. He lost his left arm in battle and found that controlling or drawing his sword out from his belt without the use of his left hand was nearly impossible. So he invented the second strap that went across his shoulder in order to facilitate that movement. Now, to the more modern side of the story - the one that sounds less intellectual and more materialistic. I was on Gilt last night and saw this most amazing beautiful belt in the Vogue March Issue sale (which, incidentally is themed "military"), and I fell in love. I obviously Googled the hell out of "belt that goes over shoulder", "shoulder belt", "military shoulder belt", and "body belt" (this one gave me some fabulous neon light reflecting bicycle belts, by the way) and finally found the name Sam Browne. So, if you know where I can find one, or if you know what the Vogue one is called or who it's by, let me know! :)
