[Nisgeis]

My Theory:

She was making a submerged down the throat attack, fired three torpedoes, then went full rudder and dived. Hatsutaka evaded and closed for an attack on the last position and layed a pattern. Torpedomen got the top two tubes closed and the third was in the process of being closed, when a DC from one of the Hatsutaka's throwers exploded in very close proximity to the hull, as the Lagarto turned hard to get out from under the DD's track. The DC caused the bow planes to jam and also due to the distortion of the pressure hull, a loss of buoyancy. Stern planes were set to full rise to try to regain attitude control, as a full dive was in progress, which accounts for the unusual positioning of the fore and aft dive planes. Possibly the watertight doors would no longer close due to distortion to the pressure hull and bulkheads.