His primary concern was ensuring that the pilots had a clear understanding of their rules of engagement.
( ( His ( primary concern ) ) ( ( was ( ensuring ( that ( ( the pilots ) ( had ( ( a ( clear understanding ) ) ( of ( ( their rules ) ( of engagement ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP$ His) (JJ primary) (NN concern)) (VP (VBD was) (VP (VBG ensuring) (SBAR (IN that) (S (NP (DT the) (NNS pilots)) (VP (VBD had) (NP (NP (DT a) (JJ clear) (NN understanding)) (PP (IN of) (NP (NP (PRP$ their) (NNS rules)) (PP (IN of) (NP (NN engagement))))))))))) (. .)))
He knew that the pilots knew their rules of engagement backwards and forwards.
( He ( ( knew ( that ( ( the pilots ) ( ( knew ( ( their rules ) ( of engagement ) ) ) ( ( backwards and ) forwards ) ) ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBD knew) (SBAR (IN that) (S (NP (DT the) (NNS pilots)) (VP (VBD knew) (NP (NP (PRP$ their) (NNS rules)) (PP (IN of) (NP (NN engagement)))) (ADVP (RB backwards) (CC and) (RB forwards)))))) (. .)))