AERIAL PHOTOS WERE BEING TAKEN OF THE MISHAP ACFT. MISSION CALLED FOR A SIMULATED WATER LNDG (ACTUAL WATER LNDG PROHIBITED) BY FLYING AS CLOSE AS POSSIBLE TO WATER. CO-PLT AT CONTROLS DESCENDED ACFT TO ABOUT 6 FT, THEN GRADUALLY REDUCED CLRNC TO 6-12 INCHES ABOVE WATER, AIRSPD 105 MPH. CO-PLT INADVERTANTLY ALLOWED ACFT TO TOUCH WATER. ON TOUCHDOWN, ACFT DECELERATED VIOLENTLY AND BROKE UP, EJECTING SEVERAL OF THE OCCUPANTS AND COMING TO REST INVERTED. EXAMINATION OF AERIAL PHOTOS SHOWS ACFT HULL AT TOUCHDOWN WAS SLIGHTLY NOSE DOWN VICE NORMAL LNDG ATTITUDE; WATER CONTACT MADE AT LOCATION OF NOSE LNDG GEAR DOORS. PHOTOS SHOW OUTWARD RUPTURING OF FWD HULL STRUCTURE, NOSE GEAR DOORS MISSING. HULL AT REAR OF STEP SHOWED TWO PARALLEL, 3-FT LONG BY 2-IN WIDE, FORE-TO-AFT AND OUTBD-TO-INBD PENETRATIONS. FLOOR OF SHALLOW LAGOON KNOWN TO HAVE SCATTERED DEBRIS FROM PETROLEM EXPLORATIONS; HOWEVER, NO POSITIVE DETERMINATION OF ACFT CONTACT WITH SUBMERGED OBJECT COULD BE MADE.