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                                                                     EXHIBIT 5.1


                                   May 5, 1999


Navistar International Corporation
455 North Cityfront Plaza Drive
Chicago, IL 60611

                   Re: Navistar International Corporation
                       Form S-8 Registration Statement
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Ladies and Gentlemen:

     I have acted as General Counsel to Navistar  International  Corporation,  a
Delaware   corporation  (the   "Company"),   in  connection  with  the  proposed
registration  by the Company of up to  6,000,000  shares (the  "Shares")  of its
Common Stock, par value $.10 per share, with associated rights, to be issued and
sold by the  Company  under a Form S-8  Registration  Statement,  filed with the
Securities and Exchange  Commission (the "Commission")  under the Securities Act
of 1933,  as amended (the "Act")  (such  Registration  Statement,  as amended or
supplemented,  is hereinafter referred to as the "Registration Statement").  The
Shares are to be issued upon the exercise of awards  granted under the Company's
1994 Performance  Incentive Plan, 1998 Interim Stock Plan, and 1998 Supplemental
Stock Plan (collectively, the "Plans").

     In that connection, I have examined such corporate proceedings,  documents,
records  and matters of law as I have  deemed  necessary  to enable me to render
this opinion.

     For  purposes  of this  opinion,  I have  assumed the  authenticity  of all
documents  submitted to me as originals,  the conformity to the originals of all
documents submitted to me as copies and the authenticity of the originals of all
documents  submitted to me as copies.  I have also assumed the legal capacity of
all natural  persons,  the  genuineness of the signatures of persons signing all
documents in  connection  with which this opinion is rendered,  the authority of
such persons signing on behalf of the parties thereto other than the Company and
the due  authorization,  execution  and delivery of all documents by the parties
thereto  other  than the  Company.  As to any  facts  material  to the  opinions
expressed  herein,  I have relied upon the  statements  and  representations  of
officers and other  representatives  of the Company and others.  For purposes of
numbered  paragraph 1, I have relied  exclusively  upon  certificates  issued by
governmental  authorities in the relevant  jurisdictions and such opinion is not
intended to provide any  conclusion  or assurance  beyond that  conveyed by such
certificates.

     The opinion expressed below is subject to the qualifications that I express
no opinion as to the  applicability  of,  compliance with, or effect of any laws
except the internal laws of the State of Illinois,  the General  Corporation Law
of the State of Delaware and the federal law of the United States of America.

     Based upon and subject to the  foregoing  qualifications,  assumptions  and
limitations  and the further  limitations  set forth below,  I hereby advise you
that in my opinion:

     (1) The Company is a corporation  existing and in good  standing  under the
laws of the State of Delaware.

     (2) The Shares are duly  authorized  and reserved  for  issuance  under the
applicable  Plan, and, when (i) the  Registration  Statement  becomes  effective
under the Act,  (ii) the Shares have been duly  executed and delivered on behalf
of the Company countersigned by the Company's transfer agent/registrar and (iii)
the Shares are issued in accordance  with the terms of the applicable  Plan upon
receipt of the  consideration  to be paid  therefor of at least $0.10 per share,
the Shares will be validly issued, fully paid and nonassessable.


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     I hereby  consent  to the filing of this  opinion  with the  Commission  as
Exhibit 5.1 to the  Registration  Statement.  In giving this  consent,  I do not
thereby  admit that I am in the  category of persons  whose  consent is required
under Section 7 of the Act or the rules and regulations of the Commission.  This
opinion  and  consent  may  be   incorporated   by  reference  in  a  subsequent
registration  statement on Form S-8 filed  pursuant to Rule 462(b) under the Act
with respect to the  registration  of additional  securities  issuable under the
Plans.

     I do  not  find  it  necessary  for  the  purposes  of  this  opinion,  and
accordingly I do not purport to cover herein,  the application of the securities
or "Blue Sky" laws of the various states to the issuance and sale of the Shares.

     This opinion is limited to the specific  issues  addressed  herein,  and no
opinion may be inferred or implied beyond that expressly stated herein. I assume
no obligation to revise or  supplement  this opinion  should the present laws of
the State of Illinois,  the General  Corporation Law of the State of Delaware or
the federal law of the United States be changed by legislative action,  judicial
decision or otherwise.

     This  opinion is  furnished  to you  pursuant to the  applicable  rules and
regulations  promulgated  under  the Act in  connection  with the  filing of the
Registration Statement.

                                   Very truly yours,

                                   /s/ Robert A. Boardman

                                   Robert A. Boardman,
                                   General Counsel


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