1
 
                                                                     EXHIBIT 5.1
 
                    [Weil, Gotshal & Manges LLP letterhead]
 
                               September 15, 1998
 
Diamond Offshore Drilling, Inc.
15415 Katy Freeway
Houston, Texas 77094
 
Ladies and Gentlemen:
 
     We have acted as counsel to Diamond Offshore Drilling, Inc., a Delaware
corporation (the "Company"), in connection with the preparation and filing by
the Company with the Securities and Exchange Commission of a Registration
Statement on Form S-3 (the "Registration Statement") under the Securities Act of
1933, as amended (the "Act"), relating to 17,682,055 shares (subject to
adjustment as described below) (the "Shares") of the common stock, par value
$.01 per share ("Common Stock"), of the Company, that may be deliverable by
Loews Corporation, a Delaware corporation ("Loews"), upon exchange of the 3 1/8%
Exchangeable Subordinated Notes due 2007 (the "Notes"), in an aggregate
principal amount of $1,150,000,000, of Loews. The number of Shares of Common
Stock that may be delivered by Loews upon exchange for the Notes is subject to
adjustment in certain circumstances as described in the Notes and in the
indenture (as supplemented by the first, second and third supplemental
indentures thereto) under which the Notes were issued. The Shares being
registered under the Registration Statement will be offered on a continued or
delayed basis pursuant to the provisions of Rule 415 under the Act.
 
     In so acting, we have examined originals or copies, certified or otherwise
identified to our satisfaction, of the Amended and Restated Certificate of
Incorporation of the Company, the resolutions adopted by the Board of Directors
of the Company authorizing the issuance of the Shares to Loews and authorizing
the preparation and filing of the Registration Statement and such corporate
records, agreements, documents and other instruments, and such certificates or
comparable documents of public officials and of officers and representatives of
the Company, and have made such inquiries of such officers and representatives,
as we have deemed relevant and necessary as a basis for the opinions hereinafter
set forth.
 
     In such examination, we have assumed the genuineness of all signatures, the
legal capacity of natural persons, the authenticity of all documents submitted
to us as originals, the conformity to original documents of all documents
submitted to us as certified, conformed or photostatic copies and the
authenticity of the originals of such latter documents. As to all questions of
fact material to this opinion that have not been independently established, we
have relied upon certificates or comparable documents of officers and
representatives of the Company.
 
     Based on the foregoing, and subject to the qualifications stated herein, we
are of the opinion that:
 
          1. The Company is a corporation duly incorporated, validly existing
     and in good standing under the laws of the State of Delaware.
 
          2. The Shares that are issued and outstanding on the date hereof have
     been duly authorized and validly issued and are fully paid and
     nonassessable.
 
     The opinions expressed herein are limited to the corporate laws of the
State of Delaware, and we express no opinion as to the effect on the matters
covered by this letter of the laws of any other jurisdiction.
 
     We hereby consent to the filing of this letter as an exhibit to the
Registration Statement and the reference to this firm under the caption "Legal
Matters" in the prospectus forming a part of the Registration Statement.
 
                                            Very truly yours,
 
                                            /s/  WEIL, GOTSHAL & MANGES LLP