 In hunting and sinking "Gambetta", Trapp achieved a notable success as commander of the first submarine to execute the first-ever underwater nighttime (and only the second nighttime) submarine attack on a vessel in the Adriatic.Just over three months later, he sank the Italian submarine at on 5 August 1915, off Pelagosa (Palagruža) Island.He also captured the Greek steamer "Cefalonia" off Durazzo on 29 August 1915.