[giantrobot]

> Don't submarine use some form of radars to figure what's around then and where are they headed?

No. When submerged they rely on navigation charts (with higher than normal bathymetric details), passive sonar, and their navigation instruments. A submerged submarine blasting out active radar and sonar to determine its position wouldn't be very stealthy.

Not every part of every ocean has complete bathymetric details. Seamounts don't necessarily move but undersea volcanos can grow in size significantly in short periods of time. A change in a few meters height can make last year's chart inaccurate today.