Letter from Admiral Sir John Fisher, Commander-in-Chief, Portsmouth (Admiralty House, Portsmouth [Hampshire]), to Rear-Admiral Prince Louis of Battenberg [Director of Naval Intelligence, later 1st Lord Milford Haven], on submarine warfare, stating that the submarine would displace the gun and revolutionise naval tactics, and suggesting that the output of submarines should be doubled at any cost. [Hand-written copy, with annotations by Fisher, written in 1911; typescript copy at CHAR 13/2/129-130].