After a short period as first lieutenant in the old destroyer , from September 1939 to April 1940, Gretton was appointed at very short notice as first lieutenant in the large modern destroyer and saw action at the
Second Battle of Narvik during the
Norwegian Campaign. From 22 April 1943 to 6 May 1943, Commander Gretton led Escort Group B7 in covering
Convoy ONS 5, considered to be the turning point of the
Battle of the Atlantic. On the return voyage Commander Gretton and Escort Group B7 successfully covered
Convoy SC 130, with no losses to enemy action and an on-time arrival that allowed his wedding to happen as scheduled. Gretton continued in command of Escort Group B7 until the summer of 1944, when it was disbanded as part of the preparations for
Operation Neptune, the naval portion of the Normandy invasion. His next posting was to the Admiralty plans division, where he worked from 1944 to 1946. ==Post war==