During World War II, he was awarded the Distinguished Service Order as a temporary major for action in Libya on 27 May 1942 at Point 171, south of Bir Hakiem commanding the 7th Field Battery, 2nd Field Regiment, Indian Artillery. The citation recommending Kumaramangalam for a Distinguished Service Order runs as follows:
4 June 1942 Captain PARAMASIVA PRABHAKAR KUMARAMANGALAM, 2nd Indian Field Regiment, 3rd Indian Motor Brigade For great courage and devotion to duty. On 27 May 1942 during the action which took place 3 miles S.E. of BIR HACHEIM, Major Kumaramangalam showed great bravery in controlling the fire of his battery under heavy enemy fire. He continually encouraged the gun detachments, and by his cool demeanour in the face of machine gun and anti-tank fire from enemy tanks undoubtedly inspired his men with the confidence with which they withstood the final tank attack. When one of his troops was over run and captured, he acquired an armoured car left at the position and tried to drive the Italian tanks away which were encircling it. Subsequently he lead a patrol back to the position and recovered three guns.
He was taken Prisoner of War by the Italians later in 1942 and held in a PoW camp in Italy. With the Italian Armistice in September 1943 he escaped on 19 November; however he was captured again in January 1944 and imprisoned, this time in Germany, where he was transferred to Stalag Luft III a high security camp for PoWs. At the end of the war in 1945, he returned to India.
Postwar
On 18 April 1946, Kumaramangalam was appointed a Member of the Order of the British Empire. He became an acting Brigadier in 1948, with the substantive rank of lieutenant-colonel, and was promoted to the substantive rank of colonel on 2 February 1951. As a brigadier, he was appointed to command a paratroop brigade on 14 February 1955, and was given command of an infantry division on 9 September 1956, with the acting rank of major-general. Kumaramangalam was promoted to substantive major-general on 1 August 1958, and appointed the Commandant of the Defence Services Staff College on 25 February 1959. He was appointed Adjutant-General on 5 October 1959, with the acting rank of lieutenant-general. Promoted lieutenant-general on 8 May 1961, he took over as General Officer Commanding, Eastern Command on 1 May 1963, with appointment as GOC-in-C, Eastern Command on 4 April 1964. On 16 November 1964 he was appointed Deputy Chief of the Army Staff, followed by appointment as Vice Chief of the Army Staff on 15 January 1965. General Kumaramangalam took over as the Chief of the Army Staff on 8 June 1966, the first Indian gunner officer and paratrooper to reach this coveted appointment. The tenure of General Kumaramangalam as Chief of the Army Staff was marked by an unpublicised but exhaustive re-organisation of the service, up-gradation of weapons, training and tactics based on the lessons learned from the 1965 War. He served in the Indian Army with distinction for 36 years until his retirement on 7 June 1969. He received the Padma Vibushan in 1970.
Views on America
General Kumaramangalam trained at the artillery school in Fort Sill, Oklahoma. From his letters it is evident he was not very impressed with the Americans. He saw them as suffering from an "aggressive inferiority complex" and cautioned a newly independent India against coming under American influence. The following is an excerpt from a letter written by him to C. Rajagopalachari in 1947:
