The pilots knew their mission was to divert aircraft, but did not know that the threat came from hijacked airliners.
( ( The pilots ) ( ( ( ( ( knew ( ( their mission ) ( was ( to ( divert aircraft ) ) ) ) ) , ) but ) ( ( did not ) ( know ( that ( ( the threat ) ( came ( from ( hijacked airliners ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS pilots)) (VP (VP (VBD knew) (SBAR (S (NP (PRP$ their) (NN mission)) (VP (VBD was) (S (VP (TO to) (VP (VB divert) (NP (NN aircraft))))))))) (, ,) (CC but) (VP (VBD did) (RB not) (VP (VB know) (SBAR (IN that) (S (NP (DT the) (NN threat)) (VP (VBD came) (PP (IN from) (NP (JJ hijacked) (NNS airliners))))))))) (. .)))
They were not even successful at diverting the aircraft from their intended course.
( They ( ( ( were not ) ( even ( successful ( at ( ( diverting ( the aircraft ) ) ( from ( their ( intended course ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBD were) (RB not) (ADJP (RB even) (JJ successful) (PP (IN at) (S (VP (VBG diverting) (NP (DT the) (NN aircraft)) (PP (IN from) (NP (PRP$ their) (JJ intended) (NN course)))))))) (. .)))