No, the hull of a submarine is two parts, the outer hull, which is made of HY-80 steel in the case of the LA class subs, and the inner hull, which is much thicker and stronger. The ballast tanks are between the hulls.
This is part of the fiberglass nose dome, the area behind it is flooded while submerged, so that the sonar dome can have full capability.
http://www.vaq34.com/junk/ussf2.jpg
This is incorrect. There is truly only one hull and the whole thing is constructed from HY-80 on LA class subs. Essentially, modern US subs are pipes with caps on both ends. The caps are generally referred to as the forward and aft elliptical bulkheads. Forward and aft of these bulkheads are the ballast tanks. You may be thinking of the older WWII type submarines that had a pressure hull and a superstructure. In the older subs the ballast tanks were wrapped around the cylindrical portion of the middle of the ship. However, this has not been an active design element since the 1960's. None of these types of subs are currently in service.
In the case of the forward ballast tank on the 688, the sonar dome is located in front of it and is connected to the inside of the ship by a watertight hatch and a trunk. In actuality, the forward end of the trunk is connected to a small room that houses the sonar transducer cabinets. In the photo it appears that most of this has either been crushed or torn away all the way back to the elliptical bulkhead.
