Commissioned Ensign 4 years later, he was designated naval aviator on 22 May 1940 and on 28 July he reported for duty with Torpedo Squadron 6 on board USS Enterprise.

Promoted to Lieutenant on 6 January 1942, he was awarded the Distinguished Flying Cross for "heroic conduct in aerial combat during the operations of U.S. forces against the Marshall Islands", on 1 February 1942.

During the Battle of Midway on 4 June he was killed as he "pressed home his attack" against the Japanese Fleet "in the face of a terrific barrage of antiaircraft fire."

Following shakedown exercises off Bermuda, Riley joined CortDiv 67 at Norfolk, Virginia, where until 6 June she trained prospective destroyer escort crews.

Departing Hampton Roads 23 June with convoy UGS-46, she crossed into the Mediterranean Sea on 10 July, fought off a German aerial attack on the 12th, and arrived off Bizerte on the 13th.

She returned to the United States 9 August, conducted sonar tests in the New London area until the 29th, then, on the 30th, sailed eastward to escort another Bizerte bound convoy.

A unit of Task Group 78.9, she herded her charges through Surigao Strait on the 9th, protected them during a series of kamikaze attacks on the 12th, and on the 13th delivered them to the transport area off the Lingayen Gulf invasion beaches.