To this day the Britannic is the largest ship on the sea floor
H.M.H.S. Britannic was originally ordered by the White Star Line as the third in her class. Her sisters included R.M.S. Titanic and the R.M.S. Olympic.
The Britannic was the largest ship lost during World War I.
Two Titanic survivors were aboard the Britannic when it sank. In the film, the fictional main character Vera Campbell is also a survivor of the Titanic, and has a nightmare of its sinking.
The film shows the ship sinking at night, with the ship finally slipping under the waves at daybreak. In reality, the ship sank in the early morning hours, shortly after breakfast.