Exhibit 5.1
                                                                     -----------



                     [Logo of Lockheed Martin Corporation]

                                August 3, 2000



Lockheed Martin Corporation
6801 Rockledge Drive
Bethesda, Maryland 20817

     Re:  Opinion re: Legality - Registration of Securities for use with respect
          to Lockheed Martin Direct Invest (the "Plan")

Ladies and Gentlemen:

     I submit this opinion to you in connection with the filing with the
Securities and Exchange Commission of a registration statement on Form S-3 (the
"Registration Statement") on the date hereof.  The Registration Statement
registers shares of common stock ("Common Stock") of Lockheed Martin Corporation
(the "Corporation") for use in connection with the Plan.  The Plan contemplates
that common stock issued in connection with the Plan may be authorized but
unissued shares or may be acquired in the open market.  As Vice President and
Associate General Counsel of the Corporation, I have examined such corporate
records, certificates and other documents and have reviewed such questions of
law as I deemed necessary or appropriate for the purpose of this opinion.

     Based upon that examination and review, I advise you that in my opinion:

     1.   the Corporation has been duly incorporated and is validly existing
          under the laws of the State of Maryland; and

     2.   the shares of Common Stock have been duly authorized and, when sold by
          the Corporation as described in the Registration Statement, will be
          validly issued, fully paid and nonassessable.

     I hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the reference to my opinion in the Registration
Statement.

                                    Sincerely,


                                    /s/ Marian S. Block
                                    -------------------
                                        Marian S. Block
                                        Vice President and Associate General
                                        Counsel
                                        Lockheed Martin Corporation