SS Nomadic is the RMS Titanic's tender ship, built in 1911 by Harland and Wolff. In the film, she brings passengers (notably Margaret Brown) to the Titanic at the French harbour of Cherbourg on her ill-fated maiden voyage. After their initial rendevous, the two ships never met again.
The real-life Nomadic exists today, preserved in her city of birth: Belfast, Ireland. She is the last maritime link to Titanic, and the last existing ship built for the White Star Line. Additionally, the work done by Harland and Wolff to restore her to her original 1911 specifications makes her the last ship worked on by the shipbuilding company.