Transcript for Seven Marines Killed During Training Exercise in Nevada
Next we turn to the tragic accident. Marine nevada dessert, suddenly a small bomb they were using to train to be warriors exploded on them. Seven marines killed. Others wounded. Abc's chief global affairs martha raddatz has been finding out what happened. Reporter: It happened in darkne. Deep in the nevada desert, some 1050 marines on predeployment training for night warfare. Using weapons every bit as deadly as if it were the real thing. The marines were firing 60 millimeter mortars. Small bombs placed into firing tubes launch over a mile. Instead, the mortar exploded while still in the firing tube. And in a flash, those seven marines were dead and more than half a dozen more wounded. Including a navy corp. Man. A team of investigators has begun the investigation to figure out what happened. Reporter: Until they find out why, the marine corp. Will suspend the use of all 60 millimetertars in tubes worldwide. This was suggest that the marine corp. Has in its preliminary assessment found there's a problem with the bomb itself. And it was not human error. Reporter: So over a year ago seven marines were killed in training when two helicopters collided near the arizona/california border. But ground training accidents are very rare, diane. Thank you so much, martha.
This transcript has been automatically generated and may not be 100% accurate.