[2] When De Mel completed his schooling, World War II had started, he joined the Ceylon Naval Volunteer Force (CNVF) and was commissioned as a probationary sub lieutenant after undergoing training at Trincomolee on 7 February 1940.
In 1950, the Royal Ceylon Navy was established, Commander De Mel transferred to a regular commission as its most senior officer and was sent to the United Kingdom for training.
The navy expanded its blue water capability and in 1960, a naval fleet undertook a deployment to the far east.
The board of investigation in to the affair recommended the dismissal of several navy officers and Admiral De Mel was relieved of command on 15 November 1960 and sent on compulsory retirement on 15 August 1961.
Avoiding arrest, De Mel was suspected of using his connections in the Indian Navy to smuggle him out of Ceylon, but surrendered to the court through his lawyer G. G. Ponnambalam when the trail of the accused started in June 1962.
In 1964, the trail at bar, found Royce De Mel along with 11 of the 24 accused guilty and sentenced then to ten years in jail and confiscation of property.