I don't know if this is an acceptable request here. But the best people to answer it would be historians, so here goes anyways.
I've had a growing fascination with warship designs of all types from the dreadnought and battleship eras (approx 1905 - 1950). But as i've read more and more about ships that were built and served in a navy i've also become interested in the ships that never were built. So, i'm looking for blueprints, online sources and perhaps even books about never-built ship designs (although my budget is strained atm, i prefer online sources).
so, hit me with whatever you've got, destroyers, cruisers, battleships, aircraft carriers, weird hybrid ships, you name it. Nationality doesn't matter either, i don't care if it's Japanese, British or Swiss, i want to see it!
I've also posted on /r/warships, here it is
My biggest recommendation for British warships that never were are David K. Brown's four-part series on British warship design. The series starts with Warrior to Dreadnought, and finishes with Rebuilding the Royal Navy, though these pre- and post-date the period you're interested in. The two you want are The Grand Fleet and Nelson to Vanguard. These books cover the design history of pretty much every single warship designed by the RN during the period, from HMS Dreadnought through to HMS Vanguard. They contains a good amount of detail on ships that were never constructed, though they might not be as thorough as works focussing entirely on a particular type of ship. Examples of such works would be Norman Friedman's works on British cruisers, battleships and destroyers, which are quite unimaginatively named (British Cruisers, The British Battleship and British Destroyers and Frigates). These are, however, somewhat more expensive than Brown's works. Samples of all of these books are available on Google Books.
First off, source recommendations are always welcome here.
Given that time period, I might suggest starting with the works of D.K. Brown, who has written extensively about warship development and design. He's a bit dry of a writer, but as a former naval architect he understands the shipbuilding and design process and you can mine his bibliography for more sources.
All of the recommendations so far have been excellent, especially Jordan's book, which is pretty expansive in coverage. Brown's work is also quite useful as he has a tendency to explain peculiar issues of design which help explain why some paper projects remained on paper.
Although they are quite expensive, William H. Garzke and Robert O. Dulin's trilogy on battleships (American, Axis & Neutral, Allied [British, French, Soviet, Dutch]) has excellent coverage of paper proposals and the design process for various battleships and battlecruisers of the interwar and Second World War periods. One of the chimeras of the interwar period was to combine both airpower and big gun armament, and R. D. Layman's The Hybrid Warship: The Amalgamation of Big Guns and Aircraft examines the often abortive attempts to marry these two concepts. The article "Design and Construction of the Yamato and Musashi" by Kitaro Matsumoto and Masataka Chihaya is an older work, but one written by two individuals involved in the construction of these BBs and they include other design proposals for Japan's superbattleships.
Here's a pretty good writeup with mock blueprints of Swedish armoured ship projects. Includes graphical representations of profiles.
Project 1047 is my favorite one. It was the Dutch plan to build 3 battlecruisers comparable to the Scharnhorst class. The design got pretty far, but it stopped when Germany invaded in 1940.
There's also the 1913 battleship proposal but it never really got very far. The acquisition plan of 4 dreadnaughts was abandoned due to the outbreak of ww1.
Friedman's US Battleships: An Illustrated Design History will give you good coverage of the Montana class (Iowa class follow-on), Lexington class (designed as battlecruisers, built as carrier), and the South Dakota class (follow-on to the "Big 5", scrapped by Washington Treaty). Navsource.org has pages for these ships that include some of the graphics from the Friedman book to give you an idea, in addition to other sources - e.g. here's a high-rez scan of a plan from the National Archives for BB-49. The HNSA site also has a set of PDF contract drawings for BB-49. For the Montanas, this forum thread offers quite a lot of visuals, being a model-oriented discussion. Wayne Scarpaci's US Battleship Conversions 1942-1965 offers more visuals of lesser-known proposals, though not at all scholarly as far as I can tell from reviews.
One of the old classics which has a lot (but not everything, of course) related to line-of-battle ships is Seigfried Breyer's Battleships and Battle Cruisers, 1905-1970 (1973) which is the English translation of a German original. I still suggest it for the line drawings and the comprehensive overview value, even though more recent work may be more accurate or detailed for particular cases.
You may already be aware of it, but one thing that might be worth looking around for is Vittorio Cuniberti's "An Ideal Battleship for the British Navy". Published in Jane's Fighting Ships in 1903 it might be the first time that anyone advocated a turbine powered all big gun battleship. I don't think it's available free online, but you might be able to get it on an interlibrary loan.
