Gianni gained international fame for his work as a diver. He worked on the case of the Spanish steamship
Cruz, sunk on
Scoglio del Catalano (Catalan Cliff) on the west coast of
Sardinia. Because the shipwreck seemed suspicious, British insurers sought divers able to check it, but none accepted the job due to its technical difficulty. Gianni accepted on condition that he would receive twice the compensation offered because of the difficulty of the job. The request was accepted and Gianni accomplished his task, finding the intentional nature of the shipwreck. He then appeared in court in
London to confirm the findings, earning recognition for himself and the superiority of Italian divers. Another famous case was the recovery in
Lake Como of the Lariana company's boat
Lecco, sunk on the evening of 18 February 1927 in the port of
Como. Gianni's most widely known achievement was probably the discovery of the wreck of the
SS Egypt, sunk in the
Atlantic Ocean off the coast of
Brest in
Brittany,
France, at a depth of about 120m and carrying a precious cargo of gold bullion and silver. Attempts to locate the ship and recover the treasure had been made by the most famous companies of the time. In the end
Lloyd's of London commissioned the credible and organized SO.RI.MA. ("Society for Maritime Recovery") founded by Commendatore
Giovanni Quaglia, who finally succeeded with the recovery ship
Artiglio ("Talon"), on which Gianni worked as chief diver and underwater operations manager. His exploits were described by journalist David Scott, who followed all the events of recoveries on behalf of the SO.RI.MA. company for
The Times of London, living aboard its ships and writing numerous articles and two books. ==Death==