<PAGE>
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                               ----------------
 
                                 SCHEDULE 14D-1
                                
                             (AMENDMENT NO. 1)     
 
                   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. 1 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") 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 14, 1994, Northrop received a letter from the Company, a copy of
which is attached hereto as Exhibit (c)(3) and incorporated herein by reference
in its entirety, and Northrop sent a letter to the Company, a copy of which is
attached hereto as Exhibit (c)(4) and incorporated herein by reference in its
entirety.     
       
ITEM 11. MATERIAL TO BE FILED AS EXHIBITS.
     
  (c)(3)   Letter dated March 14, 1994 from the Company to Northrop.     
     
  (c)(4)   Letter dated March 14, 1994 from Northrop to the Company.     
       
                               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 15, 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                                                                               SEQUENTIALLY
   NO.                         DESCRIPTION                                             NUMBERED PAGE
 -------                       -----------                                             -------------
<C>       <S>                                                                          <C>
     
  (c)(3)  Letter dated March 14, 1994 from the Company to Northrop.
                 
  (c)(4)  Letter dated March 14, 1994 from Northrop to the Company.
              
         
</TABLE>

                               Page 4 of 4 Pages





<PAGE>
 
[LETTERHEAD OF GRUMMAN CORPORATION]

                                         March 14, 1994

Mr. Kent Kresa
Chairman of the Board, President
 and Chief Executive Officer
Northrop Corporation
1840 Century Park East
Los Angeles, California 90057

Dear Kent:

     Pursuant to the request set forth in your letter to me dated March 10, 
1994, this will advise you that Grumman Corporation will provide to Northrop 
Corporation, pursuant to the confidentiality agreement between us, substantially
the same non-public information concerning Grumman that was furnished to Martin 
Marietta Corporation.

                                         Sincerely,

                                         /s/ J. ROBERT ANDERSON
                                         J. Robert Anderson

cc:  Martin Marietta Corporation
     6801 Rockledge Drive
     Bethesda, Maryland 16817
     Attention: General Counsel







<PAGE>
 
                                                          Chairman of the Board
                                                               President and
                                                         Chief Executive Officer

                                        March 14, 1994


Mr. J. R. Anderson
Vice Chairman and Chief Financial Officer
Grumman Corporation
1111 Stewart Avenue
Bethpage, NY 11714-3580

Dear Bob:

Thank you for your letter of March 14, in which you state that Grumman 
Corporation is prepared to make available to Northrop "pursuant to the 
confidentiality agreement between us" substantially the same information that 
was furnished to Martin Marietta.

As disclosed in the Northrop tender offer, dated March 14, 1994 (at p.34), it is
Northrop's position that the confidentiality agreement may not be enforced to 
prohibit or prevent Northrop's tender offer or the purchase of Grumman shares 
pursuant thereto. We wish to be clear that Northrop's receipt of confidential 
information from Grumman should not be construed as a waiver or change of this 
position.

We look forward to continuing to hold discussions on a constructive and friendly
basis.

                                            Sincerely,

                                            /s/ KENT KRESA

                                            Kent Kresa

                                            Northrop Corporation   
                                            1840 Century Park, East
                                            Los Angeles, California 90067