The 3rd RTR had a remarkable war. Its baptism of fire came in 1940 during the heroic defence of Calais where, unfortunately, after withstanding six days of continuous siege, almost three-quarters of its personnel was either killed, wounded, or 'put in the bag'. All its tanks and vehicles were lost. Some 250 officers and men were able to slip away and get back to England.

In November 1940, re-fitted and back to strength in personnel, the battalion was sent to North Africa and figured in most of the desert battles. In early 1941 just after starting out on General Wavell's first desert advance, the battalion was withdrawn from the line and sent to Greece. There, after some four months of active service in the North, where its tanks were neither strong enough or numerous enough to stop the onslaught of the German divisions, the remnants finally collected themselves in the glades of Gliphda and Daphne near Athens, prior to evacuation. All its tanks and vehicles were again lost, and only some 200 officers and men of the battalion eventually landed back in Egypt, after various adventures.

Once again made up to strength in both personnel and tanks, the battalion played a considerable part in the bloody fighting at Sidi Resegh, Bir Hackeim and Knightsbridge. It led in part the advances to Agedabia and Msus, and back to Alamein. It took part in the famous 'Left Hook' battle with the New Zealanders, making a considerable contribution to the success of the battle and subsequent forcing of the Gabes Gap and the Mareth line, and the entry into Tripoli.

Following the desert battles and marches through Agedabia for the second time and the ignominious retreat back to Alamein, the battalion enjoyed a period of rest and recuperation in the Delta.

The battalion played its part in the El Alamein battle, once again receiving heavy casualties, but went on with success at Alam Halfa and Gazala and the final advance to Enfidaville.