The general rule with British military casualties is that a body will be buried in a cemetery fairly close to the place of death. But if a man who died in action has no known grave his name is listed on a special memorial to the missing.
Most who died in the Royal Navy have no grave. If a ship was sunk few if any of the bodies would be recovered. If a man was killed but his ship survived, his body was consigned to the sea. Only in an exceptional case - if a man was wounded in action, say, and died after his ship had returned to port - would a sailor be buried in a grave. Thus the great majority of British sailors who died in the two wars have no grave and are listed on memorials.
After the First World War three naval memorials identical in form were erected at Portsmouth, Plymouth and Chatham. Later these memorials were extended to contain the names of those who died in the Second War.
The statistics are: Portsmouth 24,585 names; Plymouth 23,183 names; Chatham 18,615 names. The ratio of First to Second World War is roughly 40:60.
Denis Joseph O'Brien was born in 1890 at Whitegate, near Queenstown, the British naval base in southern Ireland. His father was serving in the Royal Navy.
He was apprenticed as a boilermaker in the naval dockyard at Haulbowline Island just across the harbour from his home. In June 1912 he joined the Royal Navy. By this time his father had died, but one younger brother and three uncles were currently in the Navy.
His widowed mother took the other children from Ireland to Portsmouth to be near her naval brothers.
In August 1914 Denis O'Brien sailed on HMS Monmouth, a rather old-fashioned cruiser hurriedly sent out to hunt for any German ships that were on the high seas at the outbreak of war.
On 1 November 1914 Monmouth, fighting against more powerful German ships, was sunk at the battle of Coronel, off the coast of Chile. There were no survivors.
The name of Denis O'Brien is recorded on the memorial at Chatham.