From Union-Castle and the War, 1914-1918 by E.F. Knight, Roll of Honour:-
Darvel, A. Private R.M.L.I. Lost in H.M.S. "Hermes".
The "Hermes" was a Highflyer class cruiser converted to a seaplane carrier in 1913. Used to ferry aircraft to France in 1914, on 30th October 1914 she was torpedoed and sunk by U-27 off Ruylington Bank, Dunkirk. 22 crew lost their lives.
The problem is that no record can be found in the Commonwealth War Graves Commission web site for an A. Darvel. I have tried numerous variations of spelling and only two records for an A. Darvell can be found but neither were serving in the R.M.L.I., both being killed in the trenches.