EXHIBIT 21 McDERMOTT INTERNATIONAL, INC. SIGNIFICANT SUBSIDIARIES OF THE REGISTRANT FISCAL YEAR ENDED MARCH 31, 1999 JURISDICTION PERCENTAGE OF OF OWNERSHIP NAME OF COMPANY ORGANIZATION INTEREST J. Ray McDermott, S.A. Panama 63 Hydro Marine Services, Inc. Panama 100 McDermott Holdings (U.K.) Limited United Kingdom 100 McDermott Marine Construction Limited United Kingdom 100 McDermott Far East, Inc. Panama 100 P.T. McDermott Indonesia Indonesia 100 McDermott South East Asia Pte. Ltd. Singapore 100 J. Ray McDermott Holdings, Inc. Delaware 100 J. Ray McDermott, Inc. Delaware 100 J. Ray McDermott International, Inc. Panama 100 J. Ray McDermott Contractors, Inc. Panama 100 J. Ray McDermott Middle East, Inc. Panama 100 J. Ray McDermott Far East, Inc. Panama 100 McDermott Incorporated Delaware 100 Babcock & Wilcox Investment Company Delaware 100 BWX Technologies, Inc. Delaware 100 B&W Services, Inc. Delaware 100 B&W Federal Services, Inc. Delaware 100 The Babcock & Wilcox Company Delaware 100 Americon, Inc. Delaware 100 Diamond Power International, Inc. Delaware 100 The subsidiaries omitted from the foregoing list do not, considered in the aggregate as a single subsidiary, constitute a significant subsidiary.