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 wanted to make sure the pilots understood their rules of engagement.
( He ( ( wanted ( to ( make ( sure ( ( the pilots ) ( understood ( ( their rules ) ( of engagement ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBD wanted) (S (VP (TO to) (VP (VB make) (ADJP (JJ sure) (SBAR (S (NP (DT the) (NNS pilots)) (VP (VBD understood) (NP (NP (PRP$ their) (NNS rules)) (PP (IN of) (NP (NN engagement)))))))))))) (. .)))