As Kasie states, Carfentanil is an extremely potent form of fentanyl that is used as a large animal tranquilizer. It is not allowed to be used on humans due to its extreme potency. It is 100 times more potent than fentanyl and 10,000 times more potent than morphine. Carfentanil-laced heroin has been responsible for thousands of deaths all over the world.
Dabney Coleman plays a WW2 veteran who was part of the Normandy Landings (June 1944). Coleman was born in 1932, so he was about 12 years old when the Normandy operation took place.