The story gets worse:

British Prime Minister Winston S. Churchill was particularly adamant that this aspect of the tragedy remain a secret. … Churchill believed that publicizing the fiasco would hand the Germans a propaganda coup.

Although the gas was mentioned in official American records, Churchill insisted British medical records be purged and mustard gas deaths listed as the result of ‘burns due to enemy action.’ Churchill’s attempts at secrecy may have caused more deaths, because had the word gone out, more victims, especially Italian civilians, might have sought proper treatment.