On military aircraft, the design went dormant during the years between the world wars. But it gained popularity in World War II, especially among pilots and crews of the Luftwaffe. Two early examples can be found on a Messerschmitt Bf 109C of 2/JG 71, and a Junkers Ju 87B-1 of 2/St.G 77, both in 1939.
The Gotha Go 242 sported the sharkmouth on the Western Front in 1915.
(Thanks to reader Noel Puzey, correction made 8/7/13.)