[1][2] He was the second Tamil to be appointed the commander of the Sri Lankan Navy after Rajan Kadiragamar in the 1960s.

He is a Counter Terrorism Fellow (CTF) and a distinguished graduate of the National Defense University.

During the Sri Lankan Civil War he led the Naval Task Force in the destruction of LTTE arms smuggling ships over a period of two years.

This was due to Sinniah opposing the purchase of a ship for twice its value and exposing corruption by the then government and defense secretary.

[5][6] His decorations include Weera Wickrama Vibhushanaya, Rana Wickrama Padakkama, Rana Sura Padakkama trice for gallantry; Vishista Seva Vibhushanaya and Uttama Seva Padakkama for meritorious service, the Fast Attack Craft (FAC) Squadron Pin and the Surface Warfare Badge.