From ‘Observing: an average day’, The Spectator, 15 April 1916:

5.10 a.m. The signaller on duty at the telephone has just said cheerfully, ‘5.30, Sir.’ I agree, and ask him if the wires are all right. They are!

5.50 a.m. Unroll the mufflers round my head and the blankets and kick off the sandbags.