The diary covers the 17th March - 23rd September 1855, and provides information about the use of steamships by the Royal Navy, a practice which was still in its infancy during the Crimean War. Johnston also records the progress of the war, including the Russian abandonment of Sevastapol on the 9th September and the fighting around the Redan redoubt shortly after. There are also descriptions of incidences of cholera onboard the transport ships.

Both letters are written to Johnston's sister Grace. The first, written between the 21st and 22nd September 1854, describes the Battle of Alma on the 20th September and Johnston's involvement in caring for injured soldiers: the envelope is labelled ' Dearest Gabriel's services to the wonded after the battle of Alma'. The second, written between the 9th and 11th September 1855, describes the end of the siege of Sevastopol.