I don’t know about 6m of water, but 6ft certainly. The interior photo’s taken at the time of recovery show, by virtue of corrosion and deposits etc, just how deeply “Swamp Ghost” has been submerged in the past. It appears that she would have been flooded up to the top of the waist gun windows during the wettest periods.

http://www.theswampghost.com/photos/2003/int/waist-right.html