When the U.S. officially entered World War II in December 1941, flight crew survival kits included blood chits printed in 50 different languages that sported an American flag and promised a reward for a safe return of a pilot. The kit might also include gifts like gold coins, maps or sewing needles. Many U.S. flight crews that flew over Asia had their “blood chit” sewn to the back of their flight jackets. Some units added the blood chit to the crew’s flight suits while other units gave the blood chit out only for specific flights. Currently, blood chits are a product of the Joint Personnel Recovery Agency. They are a small sheet of Tyvek material with an American flag and a statement in several languages indicating that the U.S. will reward anyone assisting the bearer to safety. They represent a written promise or obligation of the US Government.
While serving in the Global War on Terrorism, many U.S. service members were issued “blood chips”[citation needed] that looked similar to bearer bonds and guaranteed $500,000 for “aid and safe return”. They were issued before missions for select ground, and convoy personnel, and placed inside a soldiers ballistic vest prior to missions.

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