This drawing appears to be a rough study of early submarines on diving exercises in confined waters such as the Solent, hence the heavily beflagged marker vessel warning other shipping to keep clear. The basic conning tower on the boat to the right is indicative of an A-class boat and the one in the centre could be a B-class or early C-class. The boat at the bottom could be based on an E-class or the middle series. The black vessel appears to be a Royal Naval tug from the heavy towing bridle aft and white ensign astern, and flies a large red flag above a blue an yellow checked flag and a tricolour pennant from its foremast.