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Originally Posted by Pvt. Public
how well could a sub mask its signature if it sat as close to the bottom as possible in water shallow enough? i understand that a sandy bottom wouldnt echo, but what if its really rocky? and somewhat related, has a submarine ever settled on the bottom to avoid detection?
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Yes, it has been done. The specially outfitted USS Grayback (LPSS-574) once sat on the bottom of Haiphong Harbor in North Vietnam while she sent SEAL teams ashore to do what SEAL teams do best. There have been other instances of bottoming, but contrary to popular image, this isn't done very much. In fact it is quite rare.
A submarine has numerous suction intakes along her hull that provide a source of sea water for A/C heat exchangers, lube oil and fuel oil coolers, trim and drain systems, etc. If you sit on the bottom, these systems have to be secured and the sea chest valves shut or you will draw muck, shells, rocks and lots of other crap into the system and screw it up. Bottom the boat with a slight down angle at the stern and you risk dragging the rudder and propellers across something that might damage them and that ends your day right there. The very ends of the boat at the forward and aft torpedo rooms are single hull sections with the pressure hull exposed. Hit a rock outcropping and puncture the hull here and you have massed quantities of water in the "People Tank", also a very bad thing.
In theory at least, the right bottom conditions can weaken or distort a sonar return. But the effect is minimal and a 312' submarine makes a huge sonar target in shallow water. Many sub skippers hesitated to conduct attacks in water less than 30 fathoms (180 feet) an only the really ballsy ones (like Fluckey and O'Kane) would conduct attacks in water too shallow to submerge in.
Dave