When the water level got high enough to get up into the bottoms of the motors for the main lube oil pumps, causing grounds, the captain came aft and saw the situation and decided to take the boat shallow to allow pumping bilges. When the planesmen put a slight up-angle on the boat to come shallow the water in the bilges instantly rushed aft, greatly increasing its effect on trim (this is known as "free surface effect", later classes of subs have flood control bulkheads in engineroom lower level to prevent this) and causing an up-angle of about 45 degrees.