I have this card although mine is in considerably better condition. Interesting the ship is designated H.M.S. Olympic. I also have a similar one for a voyage from June 7 to June 13, 1919 and on that one the ship is designated H.M.T. Olympic.
I gather the ships were called into national service during wartime. HMT = Her Majesty's Transport? HMS might be a little presumptive, but leads to another question. Were these liners armed in wartime? Or was speed their best defense?