The Cavalry found out that it would mechanized on 3 November 1937

On 3 November 1937, the Cavalry was notified that five regiments would be converted to mechanized units. The famous 1st Kings Dragoon Guards only arrived in Britain from India in December. They eventually were renown for their service as an armoured car regiment, equipped with the South African-built Marmon-Herrington Mk.II's, at least at first. But in 1937, they started to convert to light tanks. They formed part of the 1st Light Armoured Brigade, converted from the 1st Cavalry Brigade. Their sister units were the 3/Hussars and 4/Hussars. The 2nd Cavalry Brigade soon was converted, as well. The 2nd brigade was probably unique, in that the same units stayed together until 1945, up to the end of the war. They were the Queen's Bays, the 9th Lancers, and the 10th Hussars. In the early months, there was much turmoil. The venerable 17th/21st Lancers became a light tank regiment with 54 tanks. At that date, they were still in India, apparently. Already, there was furious preparation for war, despite all the outward appearances that the government wanted peace. It made no difference, whether the units were in Britain or India. War preparations had started, with the focus on modernization and mechanization.