It is also detailed in "Disaster at Bari" by Glenn B. Infield, 1971, Robert Hale & Co., ISBN 07091 4312 5.
The basics are that the Luftwaffe struck the Allied shipping lying off Bari on December 2nd, 1943 including the "John Harvey" that was carrying 100 tons of mustard gas. She exploded and over 1,000 military plus "an even higher number of civilians" lost their lives.