(S (S (BASENP (DT The) (NN accident)) (VP (VP (VP (VBD occurred) (PP (IN at) (NP (BASENP (NN 4:20) (NN a.m.)) (PRN (COMMA ,) (BASENP (NNP March) (NN 21)) (COMMA ,))))) (PP (IN on) (NP (NN board) (NP (BASENP (NNP HMS) (NNP Tireless)) (PRN (COMMA ,) (BASENP (DT a) (NNP Trafalgar) (NN class) (NN submarine)) (COMMA ,)))))) (PP (IN during) (NP (BASENP (DT a) (JJ joint) (JJ US-UK) (NN exercise)) (PP (IN in) (BASENP (DT the) (NNP Arctic))))))) (PERIOD .))