"floated a C.I.D. man back into the ward posing as a patient"

A CID badge
Public DomainA CID badge
The United States Army Criminal Investigation Command is the federal law enforcement agency that investigates serious alleged crimes by civilians and military personnel attached to the U.S. Army. You might regard its agents as the detectives of the military police.

Because it was originally called the Criminal Investigation Division when it was founded during World War I at the direction of General John J. Pershing, the command’s agents and operations are still known as “CID” and certainly were referred to as such during the Second World War.

This is probably as good a place as any to recall that although Catch-22 seems to take place mostly in what we would now call the U.S. Air Force, at the time the novel takes place bombers and fighter planes were still under the aegis of the U.S. Army. They went by the name of U.S. Army Air Service between 1918 and 1926, the U.S. Army Air Corps from 1926 to 1941, and U.S. Army Air Forces from 1941 to 1947.

The U.S. Air Force only became a separate branch of the military on Sept. 18, 1947 under the National Security Act of 1947.