He became the commanding officer of the 1st Battalion , Ruhunu Regiment based in Galle with the rank of lieutenant colonel . During this time his adjutant was Lt. Tissa Weerathunga , who would later become the head of the Sri Lankan Army . Following the general election of 1956 , when S.W.R.D. Bandaranaike became prime minister , he disbanded the Ruhunu Regiment as he considered it loyal to the previous UNP government . Lt. Col. de Costa requested a transfer to his old unit the Ceylon Army Medical Corps , which was turned down . Therefore , at the age of 36 he retired from the army as one of its youngest lieutenant colonels . For his wartime service he had earned the Defence Medal and the War Medal 1939 – 1945 , and for service in the Ceylon Army , he received the Ceylon Armed Services Inauguration Medal , and the Queen Elizabeth II Coronation Medal
Queen Elizabeth II Coronation Medal
Queen Elizabeth II Coronation Medal
Rex De Costa