The large holes on either side of the hull and around the roof of the aft battery room have not been caused by internal demolition charges which would have destroyed the submarine. An isolated explosion from a build-up of gas is one possibility, but there are no obvious signs that would confirm this event.
Corrosion from leaking sulphuric acid and caustic fumes from the batteries remains a slight possibility, which requires further analysis.
The hull openings aft of the control room could be derived from fishing net hook-ups at the bow or stern. A trawler, winching its trapped nets up vertically, could have applied tremendous force to the hull. It is this force which may have caused a fatal flaw in the joint area of the heavy aft hull section. This may have been the catalyst for the corrosion we now see.
Another theory being investigated is whether the submarine had been rolled by past fishing net hookups on site. A rope, which is twice wrapped around the vessel at the aft hull, suggests that a roll may have occurred. This could explain why the conning tower and the bow are so disturbed, but that key elements, such as the conning tower net cutter, still remain in the immediate vicinity.
Such an event may have occurred in the first few decades, after the vessel descended to the seabed, when the hull was more lightly buried in the sand and perhaps retained some residual buoyancy via internal air pockets.
An analysis of the style and date of the nets is currently underway to map past contact histories. Further hull corrosion analysis is also planned to identify how stable the metal hull fabric is.