Go to the Titanic Model Research site
http://www.titanic-model.com/
They have some info on the two sisters of the Titanic, the Olympic and the Britannic.
Oh, and in her civilian guise the Britannic had the same title as her more famous sister - RMS which stands for Royal Mail Ship. HMS designates His (or Her) Majesty's Ship - and is applied to warships of the Royal Navy. The Britannic was enrolled as a naval hosptial ship during WWI and as such was given the title HMHS - His Majesty's Hospital Ship.