Submarines generally rely on acoustics to navigate underwater (the old SONAR pinging...) but they can also use towed arrays with sensors. The primary problem being that sharks tend to try to bite the towed arrays. A discussion of ways to get around this led to discussion of trouble subs have with land creatures as well...

030427-O-0000B-002 Near the North Pole (Apr. 27, 2003) -- During Exercise ICEX 2003, the Seawolf-class attack submarine USS Connecticut (SSN 22) surfaced and broke through the ice. This polar bear, attracted by the hole which can be used to find food, was seen through the sub's periscope and these photos were captured as the image was projected on a flat-panel display. After investigating the Connecticut for approximately 40 minutes, the bear left the area, with no damage to the sub or to the bear. U.S. Navy photo by Mark Barnoff. (RELEASED)

030427-O-0000B-002 Near the North Pole (Apr. 27, 2003) -- During Exercise ICEX 2003, the Seawolf-class attack submarine USS Connecticut (SSN 22) surfaced and broke through the ice. This polar bear, attracted by the hole which can be used to find food, was seen through the sub's periscope and these photos were captured as the image was projected on a flat-panel display. After investigating the Connecticut for approximately 40 minutes, the bear left the area, with no damage to the sub or to the bear. U.S. Navy photo by Mark Barnoff. (RELEASED)
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(http://www.news.navy.mil/view_single.asp?id=7749)
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Bet this potential hazard never came up in any of their risk review session!
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No problem with you adding on.
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