Time was of the essence for many military activities during the Great War. The precise firing of artillery bombardments, co-ordination of attacks by different units, and the advance by infantry under a creeping barrage all required accurate time keeping. Many officers and men were equipped with wrist and pocket watches and at times were ordered to ensure they were synchronised to the same common time. But how were they to do that?

The following detailed instructions were attached to the war diary of 1st Infantry Brigade during the Battle of the Somme in 1916. National Archives WO95/1261. Crown Copyright.