- You may be looking for the novel.
An iceberg was a piece of ice that had dropped off of glaciers.
An iceberg struck the RMS Titanic (PROSE: The Left-Handed Hummingbird), an event which subsequently grew in Earth culture. The Fourth Doctor even commented that he didn't like the word "impregnable" because it sounded too much like "unsinkable." When Harry Sullivan asked what was wrong with "unsinkable," the Doctor replied, "Oh, nothing, said the iceberg to the Titanic." (TV: Robot) According to one account, the iceberg was actually the Monk's TARDIS, and the Titanic struck it when El Ape tried to ram it. (COMIC: Follow That TARDIS!)