Shoulder flash 17th/21st Lancers

The regiment was formed in England during the interwar period by the amalgamation of the 17th Lancers and the 21st Lancers on 27 June 1922. The regiment was deployed to Meerut in India in 1936 and it was mechanised in 1938.

On the outbreak of the Second World War, in September 1939, the regiment transferred back to the United Kingdom and became part of the 1st Motor Machine Gun Brigade defending south-east England. On 12 October 1940, the 1st Motor Machine Gun Brigade became the 26th Armoured Brigade. On 9 November 1940, the brigade became part of the newly raised 6th Armoured Division, with which it served for the rest of the war.Some personnel from the regiment were detached in December to help form the cadre of the 24th Lancers.

In November 1942, the division was deployed to Tunisia for Operation Torch. Now equipped with Valentine Mk III and Crusader Mk III tanks, the regiment saw action in the Tunisia Campaign for some time, including taking heavy losses defending Thala in the Battle of Kasserine Pass in February 1943 during which fourteen tanks were put out of action.[2] After this, the regiment was withdrawn and refitted with M4A2 Sherman tanks. In April, the regiment attempted to take the Fondouk Pass during which thirty-two tanks were put out of action. The campaign in Tunisia came to an end in May 1943, with the surrender of almost 250,000 German and Italian soldiers who subsequently became prisoners of war (POWs). Most of the 6th Armoured Division (minus the 1st Guards Brigade) then deployed to the Italian Front in March 1944, and fought to breach the Gustav Line, taking part in Operation Diadem, the fourth and final Battle of Monte Cassino.The regiment advanced to the Gothic Line, and spent the winter there—at points, serving as infantry rather than as an armoured unit, due to the static nature of the trench warfare there. After the final breakthrough in April 1945, codenamed Operation Grapeshot, the regiment ended the war in Austria.