I've been doing a bit of research for the Ruritania story, and stumbled across a few interesting web sites over the past few days.
1. The US Navy's Office of Naval Intelligence (ONI) compiled a series of recognition handbooks depicting ships, submarines, and aircraft from WWI and WWII. A number are available online from the Historic National Ships Association. http://www.hnsa.org/resources/manuals-documents/single-topic/recognition-handbooks/
2. In Britain, the Airship Heritage Trust is a group promoting education and preservation regarding airships. I came across their website years ago, but revisited it just recently. They've got some neat pictures and plans of a lot of different airships from several nations. http://www.airshipsonline.com/index.htm
3. The Airships.net web site is devoted to, as the title on their page says, "The Graf Zeppelin, Hindenburg, U.S. Navy Airships, and other Dirigibles." More neat stuff. http://www.airships.net/
4. I also encountered a blog post at the Dieselpunks website about the British R100, complete with a few photos, one of which was new to me. http://www.dieselpunks.org/profiles/blogs/the-capitalist-airship-r100