Time Roaches were nesting creatures from the Vortex that were attracted by radiation that leaked into the Space Time Continuum. They took refuge in engines, where they could cause much trouble and disruption.
An infestation aboard an aircraft carrier in the 21st century took the carrier back in time two hundred years and dropped it in the middle of the Battle of Trafalgar (21 October 1805). Sailors at the time believed it to be a metal sea monster (maybe a Kraken) that appeared from out of a fog. (COMIC: Rough Waters)