The main colour study here is of a hired trawler or drifter fitted to tow a kite (observation) balloon in 1917-18. The monochrome top sketch, inscribed 'Entrance to Scapa' by Wyllie, lower right, was used by him in another drawing, see PAF1781, but as there were four channels at Scapa Flow obstructed with blockships the one in question is not easy to identify. Holm Sound between Burray and Holm was blocked by 'Aorangi' (1883) sunk 4 September 1915, 'Minieh' (1876) sunk 27 February 1915, 'Numidian' (1891) sunk 30 December 1914 and 'Thames' (1887) sunk 7 January 1915. Skerry Sound between Lamb Holm and Glims Holm was blocked by 'Almeria' (1888) sunk 20 February 1915, ' Argyle' (1872) sunk 17 September 1914, 'Elton' (1880) sunk 3 October 1914, 'Reinfeld' (1893) sunk 2 October 1914, 'Teeswood' (1882) sunk 19 September 1914 and 'Rosewood' (1889) sunk 18 September 1914. East Weddel Sound north of Burray was blocked by 'Reginald' (1878) sunk 15 September 1915, 'Gartmore' (1880) sunk 14 September 1915 and 'Lapland' (1890) sunk 16 September 1915. Water Sound between Burray and Ronaldsay was blocked by 'Clio' (1889) sunk 29 November 1914, 'Lorne' (1873) sunk 17 September 1915 and 'Pontos' (1891) sunk 30 November 1914.