The National Maritime Museum (UK) is at Greenwich. Online content includes ship images and plans, maps and charts, naval uniforms and more.
http://www.rmg.co.uk
This website has a family history section with advice for those with Scottish ancestry. There is also quite a lot of digital content including maps and broadsides, and some British military lists (army, navy and air force) for the 20th Century.
http://www.nls.uk
People, Places, Ships, Organisations and Events associated with the Royal Navy since 1660
http://www.navylist.org
This site has information on nearly 24,000 17th to 19th century naval officers and 5,000 ships. Initial searching is free and you can request a full report for a small fee.
http://www.navylist.org/index.htm
This site has a lot of British military genealogy records covering a wide range of conflicts. Most information is pay-per- view with monthly subscriptions available.
Free content includes the Japanese Prisoner of War records and a Medieval database.
http://www.forces-war-records.co.uk
Home page of the Imperial War Museums which consists of five separate museums in England covering conflict involving Britain and the Commonwealth from World War One to the present day. Explore their catalogue which provides access to their collections of over 600,000 items, including many digitised photographs.
http://www.iwm.org.uk
The National Archives Digital Microfilm means that you can download some of the most popular records from The National Archives at Kew as PDFs. Please note that these files are quite large so you will need a broadband connection.
http://www.nationalarchives.gov.uk/documentsonline/digital-microfilm.asp
ADM26 record the remittances made to relatives etc. from the pay of members of the Royal Navy after the 1795 Navy Act. A work in progress
http://www.1812privateers.org/ADM26/ADM26.html
An online index to the entries in Lieutenant John Marshall's 'Royal Naval Biography" published in London from 1823 to 1835 in 12 volumes.
http://www.agbfinebooks.com/Publications/Marshall/MarshallWeb.htm
This is a social networking site for ex British Merchant Navy seamen which includes a large database of ship images. Select Gallery and you can search by ship name for images of passenger ships, cargo ships, tankers, ferries, container ships and more.
http://www.merchant-navy.net/forum/index.php
Very detailed website with information on British naval vessels from World War One onwards. Includes lists of casualties, ships' service histories, photographs and more.
http://www.naval-history.net
Ongoing indexing of ships Masters and Mates active from 1851-1911.
http://www.history.ac.uk/gh/capintro.htm
Lots of information on the British navy from the time of Nelson including an extensive list of ships, details of men who fought at Trafalgar and officers of the Napoleonic Wars.
http://www.ageofnelson.org
Find your ancestor who fought on the English side at Trafalgar.
http://www.nationalarchives.gov.uk/trafalgarancestors
Search British First World War medal index cards, British Prisoner of War records, wills from the Prerogative Court of Canterbury 1384-1858, Royal Navy service records 1873-1923 and more.
http://www.nationalarchives.gov.uk/documentsonline