Sieker was a flight instructor during World War II, and later ran a crop spraying business in Kansas, Oklahoma and Texas. In 1955, Sieker, became a test pilot for the Lockheed U-2, a new secret jet carrying a reconnaissance camera for surveillance behind the Iron Curtain. The program was made the airplane “stealth” with a radar absorbent material. Sieker lost his life when a U-2 prototype depressurized during a high altitude flight and he was unable to deploy his parachute. He was awarded the “Agency Seal Medallion”, the highest honor of the Central Intelligence Agency, for his contribution to the early testing of aircraft used in the art of intelligence collection and war fighting.