The 3rd Royal Tank Regiment (3 RTR) was an armoured regiment of the British Army in existence from 1917 until 1992. It was part of the Royal Tank Regiment, itself part of the Royal Armoured Corps. It originally saw action as C Battalion, Tank Corps in 1917.
In 1939 it was retitled from "3rd Royal Tank Corps". In 1940, it was preparing to go to France as part of 1st Armoured Division when it was diverted at short notice to Calais. It fought during the four-day Siege of Calais, part of the Battle of France. All its tanks were lost, and many personnel killed or taken prisoner, but some escaped to Dunkirk or were evacuated from Calais before the port fell.
The regiment was subsequently rebuilt in the United Kingdom as part of 3rd Armoured Brigade, its original parent formation. Shipped to the Middle East, it was part of the 1st Armoured Brigade when it was sent to defend Greece to try to stem the German invasion in 1941.
From May to mid November 1941, there was a period of reorganization in Egypt. During this time, substantial reinforcements of both men and tanks (mostly American M3 Stuarts) were received to replace the losses incurred in Greece. From the 17th of November until the end of the year, 3 RTR took part in Operation Crusader.
In 1942, it briefly amalgamated with the 5th Royal Tank Regiment, as the 3rd/5th Royal Tank Regiment, returning to its previous title a month later. It formed part of 8th Armoured Brigade, fighting at El Alamein, and in Tunisia. It later joined 29th Armoured Brigade and fought in Normandy, the Netherlands and Germany as part of 11th Armoured Division.