<PAGE>
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                               ----------------
 
                                 SCHEDULE 14D-1
                                
                             (AMENDMENT NO. 3)     
 
                   TENDER OFFER STATEMENT PURSUANT TO SECTION
                14(D)(1) OF THE SECURITIES EXCHANGE ACT OF 1934
 
                              GRUMMAN CORPORATION
- --------------------------------------------------------------------------------
                           (NAME OF SUBJECT COMPANY)
 
                           NORTHROP ACQUISITION, INC.
- --------------------------------------------------------------------------------
                                    (BIDDER)
 
                    Common Stock, $1.00 par value per share
                       (Including the Associated Rights)
- --------------------------------------------------------------------------------
                         (TITLE OF CLASS OF SECURITIES)
 
                                    40018110
- --------------------------------------------------------------------------------
                     (CUSIP NUMBER OF CLASS OF SECURITIES)
 
                            Richard R. Molleur, Esq.
                              Northrop Corporation
                             1840 Century Park East
                             Los Angeles, CA 90067
                                 (310) 553-6262
 
                                    COPY TO:
 
                             Karen E. Bertero, Esq.
                            Gibson, Dunn & Crutcher
                             333 South Grand Avenue
                             Los Angeles, CA 90071
                                 (213) 229-7000
- --------------------------------------------------------------------------------
                 (NAME, ADDRESS AND TELEPHONE NUMBER OF PERSON
     AUTHORIZED TO RECEIVE NOTICES AND COMMUNICATIONS ON BEHALF OF BIDDER)
 
                           CALCULATION OF FILING FEE
- --------------------------------------------------------------------------------

<TABLE>
<CAPTION>
           TRANSACTION VALUATION*                       AMOUNT OF FILING FEE**
<S>                                                     <C>
              $2,104,030,800.00                              $420,806.16
</TABLE>

- --------------------------------------------------------------------------------
 
*  For purposes of calculating fee only. Assumes purchase of 35,067,180 shares
   of Common Stock, $1.00 par value per share, of Grumman Corporation at $60.00
   per share.
 
** 1/50th of 1% of Transaction valuation.
 
[_]CHECK BOX IF ANY PART OF THE FEE IS OFFSET AS PROVIDED BY RULE 0-11(A)(2)
   AND IDENTIFY THE FILING WITH WHICH THE OFFSETTING FEE WAS PREVIOUSLY PAID.
   IDENTIFY THE PREVIOUS FILING BY REGISTRATION STATEMENT NUMBER, OR THE FORM
   OR SCHEDULE AND THE DATE OF ITS FILING.
 
Amount previously paid: Not Applicable              Filing party: Not Applicable
                                                       
 
Form or registration no.: Not Applicable            Date filed: Not Applicable
                                                        
 
                               Page 1 of 4 Pages

<PAGE>
 
   
  This Amendment No. 3 amends and supplements the Tender Offer Statement on
Schedule 14D-1, dated March 14, 1994 (the "Schedule 14D-1"), of Northrop
Acquisition, Inc. (the "Purchaser") and Northrop Corporation ("Northrop"), as
amended, filed in connection with the Purchaser's offer to purchase all of the
outstanding shares of Common Stock, par value $1.00 per share, of Grumman
Corporation, a New York corporation (the "Company"), and the associated
preferred stock purchase rights, as set forth in the Schedule 14D-1.     
 
ITEM 3. PAST CONTACTS, TRANSACTIONS OR NEGOTIATIONS WITH THE SUBJECT COMPANY.
   
  On March 28, 1994, Northrop received a letter from the Company, a copy of
which is attached hereto as Exhibit (c)(7) and incorporated herein by reference
in its entirety.     
 
ITEM 11. MATERIAL TO BE FILED AS EXHIBITS.
            
  (c)(7)   Letter dated March 28, 1994 from the Company to Northrop.     
 
                               Page 2 of 4 Pages

<PAGE>
 
                                   SIGNATURE
 
  After due inquiry and to the best of my knowledge and belief, I certify that
the information set forth in this statement is true, complete and correct.
   
Dated:March 28, 1994     
 
                                        NORTHROP CORPORATION
 
                                        /s/ Richard R. Molleur
                                        ----------------------------------------
                                        Name: Richard R. Molleur
                                        Title: Corporate Vice President
 
                                        NORTHROP ACQUISITION, INC.
 
                                        /s/ Richard R. Molleur
                                        ----------------------------------------
                                        Name: Richard R. Molleur
                                        Title: Vice President and Secretary
 
                               Page 3 of 4 Pages

<PAGE>
 
                                 EXHIBIT INDEX
 
          

<TABLE>
<CAPTION>
 EXHIBIT
   NO.                               DESCRIPTION
 -------                             -----------
 <C>      <S>    
  (c)(7)  Letter dated March 28, 1994 from the Company to Northrop.
              
</TABLE>


                               Page 4 of 4 Pages





<PAGE>
 
[LETTERHEAD OF GRUMMAN CORPORATION]
                                                            Dr. Renso L.Caporali
                                                       Chairman of the Board and
                                                         Chief Executive Officer


                                 March 28, 1994


Martin Marietta Corporation
6801 Rockledge Drive
Bethesda, Maryland 26817

Northrop Corporation
1840 Century Park East
Los Angeles, California 90067

    Re: Rules and Procedures for Submission of Proposals
        ------------------------------------------------

Gentlemen:

    The Board of Directors of Grumman Corporation (the "Company") has determined
that it is in the best interests of the shareholders of the Company to have free
and open competitive bidding for the Company.

    Northrop Corporation ("Northrop") has requested, in a letter dated March 23,
1994, that there be "a free and open competitive bidding" and that the Company
"take such actions as may be necessary and appropriate . . ." to achieve this.
Martin Marietta Corporation ("Martin Marietta") has recognized, in a letter
dated March 25, 1994, that "whatever steps Grumman takes regarding the Martin
Marietta and Northrop offers are, of course, Grumman decisions alone" and has
requested that it be advised promptly "if Grumman decides to establish bidding 
procedures".

    It is the strongly held view of the Board of Directors that this process
must be conducted in an open, fair and orderly manner. The interests
 of our
shareholders, employees, customers, suppliers, communities and the public
generally can and will be best served by such an approach. The Board of
Directors is mindful that the process in which the Company is currently engaged
does present certain risks, particularly; if the process is prolonged, including
disruption to


<PAGE>
 
the Company's business and overall uncertainty among the Company's 
constituencies as to the Company's future.  In order to mitigate these risks, 
the Board of Directors believes that the most prudent course of action is to 
bring this process to a prompt and orderly close.

    Accordingly, the Board of Directors has established the rules and procedures
specified below for receiving proposals to acquire the Company ("Proposals").
The procedures are designed to constitute a single and final round of bidding,
and each of you should submit your best and highest offer.

    The purpose of this letter is to invite each of you to submit Proposals,
pursuant to such rules and procedures. The Board of Directors believes that
agreement to such rules and procedures is critical to mitigating the risk of the
process in which the Company is now engaged and, accordingly, submission of a
Proposal will constitute for all purposes an agreement to be bound by such rules
and procedures.

    The following rules and procedures will govern the submission of Proposals:

    1. Proposals should be in the respective forms attached and should be
addressed and delivered in a sealed envelope to the Board of Directors of the
Company: c/o Gene T. Sykes, Goldman, Sachs & Co., 85 Broad Street, New York, New
York 10004. Proposals must be received on Thursday, March 31, 1994 at 5:00 p.m.
New York time (the "Submission Date"), unless extended by notice. You may not
make any proposal, or modify or amend any pending Proposal, to purchase the 
Company, except as prescribed herein.

    2. Until we have accepted one of your Proposals, we will not, except as may 
be required by law, publicly disclose the terms of either of your Proposals or 
communicate them to the other of you.  Submission of your Proposal constitutes a
representation that you have kept and will keep your Proposal confidential until
9:00 a.m. New York time Monday, April 4, 1994 and that you have no knowledge of 
the other's Proposal.

    3. The Agreement and Plan of Merger currently in effect between the Company 
and Martin Marietta without any

<PAGE>
 
change (except as to the price per Share as defined therein and as to language 
amending upon acceptance the existing Merger Agreement to reflect such price per
Share) is to be used by Martin Marietta as specified in submitting the attached 
form of Proposal for execution by Martin Marietta.  The form of the Agreement 
and Plan of Merger submitted by Northrop to Grumman, pursuant to the letter 
dated March 23, 1994 from Northrop's counsel to the Company's counsel, without 
any changes (except as to price per Share as defined therein) is to be used by 
Northrop as specified in submitting the attached form of Proposal for execution 
by Northrop.

    4. It is the intention of the Board of Directors that the winning Proposal
will be accepted as promptly as possible after 5:00 p.m. New York time Thursday,
March 31, 1994. It is requested that each of you be available the week-end
commencing 5:00 p.m. New York time in the case of Martin Marietta to execute an
amendment to the Agreement and Plan of Merger and in the case of Northrop to
execute the Agreement and Plan of Merger as specified in Paragraph 3. Each
Proposal will be irrevocable until 9:00 a.m. New York time on Monday, April 4,
1994.

    5. The Board of Directors will accept the Proposal which it determines in
its reasonable good faith judgement is the best value reasonably obtainable for
shareholders of the Company. A Proposal will be accepted only by a written
acceptance signed by the Chairman of the Board, or other official of the Company
specifically authorized by the Board of Directors.

    The Board of Directors reserves the right, insofar as necessary in the
proper exercise of its fiduciary duties, to change the rules and procedures set
forth in this letter. If the Board of Directors modifies these rules and
procedures, it intends promptly to notify both of you orally, with confirmation
in writing.

                                        Very truly yours,

                                        BOARD OF DIRECTORS
                                        GRUMMAN CORPORATION

                                        By: /s/ RENSO L. CAPORALI
                                                -----------------------------
                                                Renso L. Caporali
                                                Chairman


<PAGE>

 
                               FORM OF PROPOSAL

                              FOR MARTIN MARIETTA




Board of Directors
Grumman Corporation
c/o Gene T. Sykes
Goldman, Sachs & Co.
85 Broad Street
New York, NY 10004

Lady and Gentlemen:

    Martin Marietta Corporation hereby offers, pursuant to and in accordance 
with the rules and procedures in your letter to us dated March 28, 1994 (the 
"Procedures"), to amend the Agreement and Plan of Merger, dated as of March 6, 
1994, among Martin Marietta Corporation, MMC Acquisition Corp. and Grumman 
Corporation (the "Merger Agreement"), to increase the price Acquisition would 
pay to $______ per Share pursuant to and otherwise in accordance with the Merger
Agreement.

    This offer shall be irrevocable until 9:00 a.m. New York time on Monday
April 4, 1994. The execution and delivery of this Proposal, pursuant to and in
accordance with the Procedures, and the consummation of the transactions
contemplated hereby and thereby have been duly and validly authorized by the
boards of directors of Parent and Acquisition and by Parent as sole shareholder
of Acquisition, and no other corporate proceedings on the part of Parent or
Acquisition are necessary to authorize this offer or the amendment to the Merger
Agreement contemplated hereby. (Defined terms used herein shall have the
meanings specified in the Merger Agreement.)

    Acceptance of this offer by Grumman Corporation in accordance with the 
Procedures shall constitute an amendment to the Merger Agreement to change in 
the second WHEREAS clause $55.00 to $______.  The Merger Agreement, except as so
amended, shall remain in full force and effect.

                                        Sincerely yours,



                                        -----------------------
                                        Norman R. Augustine
                                        Chairman of the Board and
                                        Chief Executive Officer



<PAGE>
 
                               FORM OF PROPOSAL
                                 FOR NORTHROP

Board of Directors
Grumman Corporation
c/o Gene T. Sykes
Goldman, Sachs & Co.
85 Broad Street
New York, NY 10004

Lady and Gentlemen:

    Northrop Corporation hereby offers, pursuant to and in accordance with the 
rules and procedures in your letter to us dated March 28, 1994 (the 
"Procedures"), to amend the form Agreement and Plan of Merger, dated as of March
24, 1994, among Northrop Corporation, Northrop Acquisition, Inc. and Grumman 
Corporation submitted to you, pursuant to the letter dated March 23, 1994 from 
our counsel to your counsel (the "Merger Agreement"), to increase the price 
Acquisition would pay to $_____ per Share pursuant to and otherwise in 
accordance with the Merger Agreement.

   This offer shall be irrevocable until 9:00 a.m. New York time on Monday,
April 4, 1994. The execution and delivery of this Proposal, pursuant to and in
accordance with the Procedures, and the consummation of the transactions
contemplated hereby and thereby have been duly and validly authorized by the
boards of directors of Parent and Acquisition and by Parent as sole shareholder
of Acquisition, and no other corporate proceedings on the part of Parent or
Acquisition are necessary to authorize this offer or the amendment to the Merger
Agreement contemplated hereby. (Defined terms used herein shall have the
meanings specified in the Merger Agreement.) 

    Acceptance of this offer by Grumman Corporation in accordance with the
Procedures shall constitute an amendment to the Merger Agreement to change in
the second WHEREAS clause $60.00 to $____ and the Merger Agreement, so amended,
shall be in full force and effect.

                                     Sincerely yours,


                                     _________________________
                                     Kent Kresa
                                     Chairman of the Board and
                                     Chief Executive Officer