Inscribed by the artist, as title, lower right and with the measurements below '11 x 9' [inches]. During the World War I Wyllie was often at sea with the Navy. This enabled him to make a huge contribution to recording many aspects of the war, although he was not present at any major actions. He exhibited twenty related pictures at the Royal Academy, illustrated and co-authored two books ('Sea Fights of the Great War', 1918 and 'More Sea Fights of the Great War', 1919), produced etchings and a very large number of watercolours and drawings, such as this one which is a preliminary study for a plate in 'More Sea Fights of the Great War' entitled 'Light Cruiser passing through Blackrock Gate, Firth of Forth'.

The Blackrock Gate was a wartime defence boom - controlled by the trawlers seen here - that ran between the Eastern Craigs, just east of Leith harbour, and Long Craig, Inchkeith Island, in the middle of the Firth of Forth. The light cruiser passing inward through the boom beyond the third trawler is one of the early 'C'-class ships, the first of which was completed in August 1916.The dark shape above in the sky is an observation balloon or coastal airship, which is clearer on the finished version of the drawing. In the summer of 1915 Wyllie was with the fleet in the Firth of Forth, and a day after witnessing and recording target practice in the Moray Firth he recalled:

'When the target practice was over our subdivision steamed away for the Forth, still screened by the escorting destroyers ahead and on both sides. Early next morning, putting my head out of the scuttle, I saw Arthur's Seat and Auld Reekie, with the Castle and the Calton Hill half hidden in the mists. We were passing through the Blackrock Gate, and long lines of moored trawlers with their nets and floats stretched away towards Granton, where Admiral Startin had his base of trawlers, motor-launches and decoy ships. The water had changed from blue to mud colour ...'. (W. D. Kirkpatrick, C. Owen and W. L. Wyllie, ‘More Seat Fights of the Great War' [London: Cassell & Company Ltd., 1919]).