The Prometheus was traveling off the coast of Norway deep under the ocean. It was being tracked by a United States military post who just noticed strange readings.
Unbeknownst to the Prometheus Crew the super villain Hypnotia snuck aboard and planted a Bio-Conversion Device. The captain noticed strange readings and found the hidden woman. She incapacitated them and covered the entire crew in a strange substance. She then used a laser to cut a hole in the hull and sank the sub.
The sub drifted towards the coast of Scotland where it sank and set on the bottom of the ocean. It sat there for a year while the crew were converted into radioactive zombies.