Thrasher began her service by heavily damaging the French fishing vessel Virgo Fidelis in the Bay of Biscay, while in transit to the Mediterranean.
The Virgo Fidelis was beached, but declared a total loss.
 Once in the Mediterranean she sank a number of ships, including three Greek sailing vessels, one of which was the San Stefano; the Italian sailing vessel Esperia; the Italian merchants Attilio Deffenu, Fedora, Gala, Penelope, Lero, Sant'Antonio and Padenna; the German army cargo ship Atlas; the Italian tugs Pilo and Roma; and the Italian aviso Diana.
She also unsuccessfully attacked the German transport Ankara and the German merchant Arkadia.
 She also attacked the German barge F 184, but was forced to withdraw due to return fire.
In July 1942, Thrasher was bombed in error by a British Fairey Swordfish aircraft off Port Said, Egypt, causing damage that took a month to repair.

Thrasher sank 20,000 long tons (22,000 short tons; 20,000 t) of enemy shipping during the Mediterranean campaign.
Thrasher began her service by heavily damaging the French fishing vessel Virgo Fidelis in the Bay of Biscay, while in transit to the Mediterranean. The Virgo Fidelis was beached, but declared a total loss.  Once in the Mediterranean she sank a number of ships, including three Greek sailing vessels, one of which was the San Stefano; the Italian sailing vessel Esperia; the Italian merchants Attilio Deffenu, Fedora, Gala, Penelope, Lero, Sant'Antonio and Padenna; the German army cargo ship Atlas; the Italian tugs Pilo and Roma; and the Italian aviso Diana. She also unsuccessfully attacked the German transport Ankara and the German merchant Arkadia.  She also attacked the German barge F 184, but was forced to withdraw due to return fire. In July 1942, Thrasher was bombed in error by a British Fairey Swordfish aircraft off Port Said, Egypt, causing damage that took a month to repair.
Thrasher sank 20,000 long tons (22,000 short tons; 20,000 t) of enemy shipping during the Mediterranean campaign.
HMS Thrasher (N37)