At the beginning of the war it was freely stated that the one ship a submarine could not fight was the submarine. This theory, like so many others, went by the board in the process of time. Finally the notion was completely reversed. Allied underwater craft ferreted out many an enemy submersible. Indeed, if we accept the authority of Rear-Admiral S. S. Robison, of the United States Navy, they did “more than any other class of vessel” to defeat the U-boats. The French and Italians name the units of their underseas navy. They are not vague, impersonal things denoted by a letter and a number, after the fashion of an inhabitant of Portland Prison. The first recorded action between submarines took place in June 1915. It remains one of the mysteries of the war. The Italian submarine _Medusa_, after carrying out several daring reconnaissances, was torpedoed by an Austrian submersible of almost similar type and size. The _Medusa_ was quite a small boat, built at Spezzia in 1911, with a displacement of 241 tons on the surface and 295 tons below water. Her crew numbered seventeen. She was scouting in the Adriatic when the incident occurred, and we must presume her to have been comparatively close to the enemy without being aware of the fact, otherwise her action is unaccountable. For some reason or other she came to the surface, whereupon the commander of the Austrian U-boat sighted her through his periscope and torpedoed her. An officer and four men were picked up. According to a later report, divers were sent down to examine the condition of the _Medusa_ with a view to salvage operations. They made the startling discovery that the wreck of an Austrian submersible was lying close to that of the Italian, suggesting that the two vessels had participated in a duel in which both had got a fatal shot home and neither was the victor.