An aerial-view wash study of Fort Blockhouse, looking across the Solent towards the Isle of Wight. The vessel in the foreground is to a larger scale (i.e., a separate drawing on the same sheet) and probably intended to be the submarine depot ship 'Forth' (1886): it has a submarine alongside. Above its funnel and mast alongside the Fort's berthing area is the Haslar Floating Dock (renamed AFD 2 in 1925): this arrived in late 1906 and continued to serve here until 1959. The defensive boom across the entrance to Portsmouth Harbour can be seen on the left, suggesting this is probably a First World War view. Wyllie was perfectly capable of doing such aerial 'prospect' drawings from sketches made on the ground but did have opportunity to make ascents in balloons and aircraft, as well as using photographs; so it is not always easy to know what method he used in particular cases.