Cannonball is one of the many crew members who was onboard the HMS Shortcut. Although his real name is Joe Shooter, he goes by his nickname Cannonball and is third mate on the HMS Shortcut. He is introduced in The Mysterious Benedict Society and the Perilous Journey.
Cannonball has a brilliant personality with a fabulous sense of humor. He likes the children and Phil Noland. He also shares the thought along with Nolan that the rich Mr. Pressius, and all the businessmen are "bullfrogs." He has a very adventurous spirit much like Kate and is also known to be extremely kind such as when he took care of Madge for Kate.