Now I know why I don't draw subs.
Modern subs aren't that bad in shape, but it can be really hard to get details on anything below the "waterline", like valves etc. These refinements came because I found a few pictures of a Collins in drydock. Previously I'd simply assumed that the grating in front would be mimicked in the back, whereas the grating was actually much smaller than I'd assumed, and in the back there's two circular valves. Also, the side array is slightly further up the hull than originally.
But those are all things you'd never know without hi-res pics of a boat in drydock.