The first sinking of an aircraft carrier was the HMS Courageous on September 17, 1939 off the coast of Ireland, by the German U-Boat, U-29. She was also the first British warship to be lost in the war
IJN Shoho went down on 7 May 1942 but she was the first Japanese aircraft carrier to be sunk in the Pacific War.
The first to sunk in war.
31 October 1914
H.M.S Hermes, British, Highflyer class Second Class Cruiser converted to Seaplane Carrier.
Torpedoed by German submarine U27 whilst acting as an aircraft transport between Dover and France. First torpedo struck from a range of c.300 yards and as the cruiser was sinking by the stern a second torpedo hit her and she then sank quickly.
sorry just a small point but I think you mean the first in Pacific War.