Enemy in Sight - J.E. Macdonnell #04. J.E. Macdonnell's Royal Australian Navy World War II Fiction, #4

"That boat back there is a complete submarine - in miniature. About fifty feet long, including propeller, rudder and hydroplanes. That reduces your living space to something nearer thirty-five feet. You have no torpedo tubes, no armaments. You're not meant to be found or to fight a battle. From now on you're a sneaker. Inoffensive - until you release your side cargoes. Each one of those holds four tons of amatol explosive and a time clock.
You drop those under that Jap cruiser's bottom and then run for your life."Peter Bentley had three weeks to learn to handle the midget submarine - three weeks to accomplish the secret and deadly mission that could be the turning point of the whole war.