where a u.s. marine corps aircraft crash has killed three marines, and injured 20 others. the crash happened earlier this morning during a joint military trail more than 2500 troops from around the world according to the australian defense forest, the u.s. marines said the cause is under investigation and recovery efforts are ongoing. nbc joins us. what more do we know? >> lindsey, what we know is out of the 20 marines that were injured, five are set to be in serious condition. we know that these marines were taken to the mainland to a hospital there. some underwent surgery. as you mentioned, this was a multinational training exercise that was happening. it is the largest happening in the northern territory that is led by the australian army. while this is incredibly tragic,