He was educated at Blundell's School in Tiverton, where he won a bursary, and, in October 1942, he gained a Macbride Open Scholarship to Hertford College, Oxford, to read geography.

After gaining his green beret, Jenkins was posted to Vis, off the Dalmatian coast, the only Yugoslav island in Allied hands.

43 (Royal Marine) Commando were supporting Tito's partisans and, as a subaltern with "E" Troop, he took part in a number of raids on the German garrisons of the other islands.

In October 1944, 43 Commando disembarked at Gruz Harbour, near Dubrovnik, as part of "Floydforce" and Jenkins's troop was deployed inland to harry the retreating Germans.

43 Commando went to Italy in January 1945 and, two months later, as part of the last major offensive of the Italian campaign, it moved up to its new front on the river Reno, north of Ravenna.

As reported in Jenkins' obituary: In the early hours of 18 April, 43 Commando passed through 2 Commado’s position with the aim of clearing a pumping station and the fortified houses that dominated the surrounding country.

When Jenkins had seen his troops into their new position, a doctor removed some metal splinters from his neck; the bullet that had knocked him down was discovered lodged among the biscuits in his 24-hour pack.He was awarded the Distinguished Service Order for his actions.