An AGRA usually had three medium artillery regiments, one heavy artillery regiment and one field artillery regiment. It was commanded by a brigadier and was transferred at need from corps to corps within an army. Each corps in the line usually had an AGRA and when especially heavy fire support was needed, one AGRA could be used to reinforce another, as in Operation Baytown, the initial attack on the Italian mainland, when two AGRAs fired across the Straits of Messina from Sicily or in Operation Undergo, the battle for Calais in 1944. As the British Army manpower shortage developed, the weight of fire that an AGRA could add to an attack became increasingly important.