In 1910 the Italian navy decided to build a class of diesel-electric submarines of their own, previous to this all Italian built submarines were gasoline-electric powered. The Medusa class consisted of eight submarines, 147' long with a surface displacement of 248 tons. They carried two 17.7" (450mm) bow tubes with two reloads. Medusa herself was the second of the eight launched, she took to the water on July 30, 1911 at the Fiat yard in La Spezia, Italy. On June 10, 1915 Medusa became the first submarine to be a victim of another submarine.

SMS UB-15 was built at A.G. Wesser in Bremen, Germany, launched Nov. 9, 1914 and commissioned into the Kaiserliche Marine on Apr. 11, 1915. Shortly thereafter the boat was disassembled and shipped by rail to Pola Naval Base. The major naval instillation of the Austro-Hungarian Empire, UB-15 was recommissioned as KuK
U-XI on June 4, 1915, but due to training the German crew was retained. Her German commander was Oberleutnant zur See Heino von Heimburg, who would sink over 44,000 tons of shipping including HMS E-20 and the transport Royal Edward, the latter went down with over 1,000 troops on board.

Medusa and U-XI (UB-15) were both in the waters off Venice, Italy, apparently unknown to each other. The commanding officer of Medusa, Tenente di vascello (Lt.) Vittori, raised his periscope and searched the horizon, seeing nothing he brought his boat to the surface. In U-XI von Heimburg also raised his periscope and to his surprise saw the Italian on the surface. Medusa was behind his boat and not having any stern tubes he brought his boat around and from close range launched one torpedo.

According to von Heimburg when the torpedo left the tube his boat "popped up like a jack-in-the-box", having never fired a torpedo from such a small boat this was something he was not prepared for. He scrambled his men forward and the boat came back under control. When he came to periscope depth he could see nothing but a cloud of smoke where the other submarine had been. Upon coming to the surface he found only five survivors of the twenty-two man crew, when they were picked up von Heimburg learned the identity of his victim. The survivors were taken prisoner and taken to Pola, the Italians were informed of the sinking and the prisoners through an official communiqué from the Austrians. The official announcement of the sinking came from the Italian Ministry of Marine on June 17.

On June 18 an Austrian crew took control of the boat and von Heimburg went on went on to continue his deadly career. Medusa was his first victim, before the war was over twenty-two others would fall to him. He survived the war winning the highest decorations in the navy and served in Hitler's Kriegsmarine rising to the rank of Vizeadmiral. After the war he was captured by the Soviets and taken to a POW camp near Stalingrad where he died in 1945.

In 1931 the Italian Navy launched a second submarine named Medusa, in a strange turn of fate her end was almost a mirror image of the original Medusa. While conducting sea trials near Pola on Jan. 30, 1942 the British submarine HMS Thorn N-11 fired several torpedoes at the boat, which like the first Medusa was on the surface. Only one out of four fired hit the boat, but that was enough to cause her to exploded and sink taking all but two men with her.