"Titanic And Her Sisters Olympic and Britannic" needs to be read with care. I have a copy myself. While the text and the historical work is decent, whoever gathered together the photos didn't bother with some elementary fact checking to get the captioning right, and the result was a list of embarrassing mistakes.
Hell, I saw one photo of what was obviously the Aquitania in her hospital ship livery which was captioned as being the Britannic.