I am not sure what he was doing in Portsmoth if he was a serving RE soldier. He was not a professional soldier, he had been a Postmaster for many years, and was 52 years old when he died. His home and family were in Dublin, and his body appears to have been brought back to Ireland for burial. It is unclear on cause of death " found dead in Portsmouth", but I cannot find any news report in Irish or English papers
1868 Jan 4. Born Armagh
1897 Feb 17 Married in Dublin to Elizabeth Anne Alexander
1911 Census, Carlyle Williams was an Overseer of the Dublin Postal District, G.P.O, Dublin, living at 8, Manor Place, Grangegorman.
He had been was married for 14 years, and was the father of 6 children.
1916 May 10 enlisted (from regimental number)
1920 The 4th Fortress Company, Royal Engineers was based in Gosport
1920 Feb 22 Died CWCG . Husband of Elizabeth A. Williams, of 8, Gardiner Place, Dublin. An entry on a military card says "found dead in Portsmouth", but I can find no further information on cause of death, as Death Cert will have been issued in England.
British Soldiers died in Ireland