GAO provided a supplement to its report on the April 1989 explosion aboard the U.S.S. Iowa, focusing on the Sandia National Laboratory's independent review of the Navy's technical analysis of the explosion. GAO found that: (1) Sandia could neither confirm nor disprove the Navy's conclusion that a deliberate act caused the explosion, nor could it could prove or disprove the Navy's contention that foreign material on the rotating band of the projectile was evidence of an improvised explosive device; (2) although the Navy concluded that impact and compression of the bag charges were not contributing factors in the explosion, it could have been a factor, since a significant overram occurred; (3) due to the lack of evidence and other physical factors, it may be difficult to ever fully resolve the many unknowns and develop a clear and unambiguous explanation of the events that occurred; and (4) there was no explicit evidence that the hypothetical chemical ignition device was present in the center gun room.