Rajapaksa joined the Sri Lanka Army as a Cadet Officer on April 26, 1971,
commissioned as a second lieutenant on May 25, 1972
he served with the Sri Lanka Sinha Regiment and the Rajarata Rifles before being transferred to the Gajaba Regiment upon its formation in 1983 with the amalgamation of the Rajarata Rifles and Vijayabahu Infantry Regiment.
Rajapaksa has received awards for gallantry from three Presidents of Sri Lanka, J.R. Jayewardene, Ranasinghe Premadasa and D.B. Wijetunga.
He had followed signal young officers course in school of signals at Rawalpindi; Infantry company commanders course in Queta; Jungle warfare and counter insurgency course in Assam; Command and Staff course at Defence Services Staff College in Welington; and Advanced Infantry Officers course at Fort Benning.
He served in the battlefronts of Jaffna, participating in Operation Liberation, the offensive mounted to liberate Vadamarachi from LTTE in 1987. He also commanded the same battalion in Operation "Strike Hard" and Operation Thrividha Balaya in 1990.
He was promoted to lieutenant colonel, and served as the Commandant of the Kotelawala Defence Academy at the time of his retirement in 1992.
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