<PAGE>
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                               ----------------
 
                                 SCHEDULE 14D-1
                               
                            (AMENDMENT NO. 11)     
                                       
                                    AND     
                                  
                               SCHEDULE 13D     
 
                   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.
                              
                           NORTHROP CORPORATION     
- --------------------------------------------------------------------------------
                                    (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>
              $2,174,165,160.00                              $434,833.03
</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 $62.00
   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
                         
                      (continued on following pages)     
 
                               Page 1 of 4 Pages

<PAGE>
 
                                    
    CUSIP NO. 400 181 103         14D-1     
    
 1     NAME OF REPORTING PERSONS S.S OR I.R.S. IDENTIFICATION NOS. OF ABOVE
       PERSONS     
 
           NORTHROP ACQUISITION, INC.
 
- --------------------------------------------------------------------------------
    
 2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                 (a) [_]
                                                                         (b) [_]
 
- --------------------------------------------------------------------------------
    
 3     SEC USE ONLY     
 
- --------------------------------------------------------------------------------
    
 4     SOURCE OF FUNDS*     
 
           BK
 
- --------------------------------------------------------------------------------
    
 5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
       ITEM 2(e) or 2(f)                                                     [_]
 
- --------------------------------------------------------------------------------
    
 6     CITIZENSHIP OR PLACE OF ORGANIZATION     
 
           DELAWARE
 
- --------------------------------------------------------------------------------
    
 7     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     
 
           DIRECTLY: 31,585,201
 
- --------------------------------------------------------------------------------
    
 8     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES CERTAIN SHARES*
                                                                             [_]
 
- --------------------------------------------------------------------------------
    
 9     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)     
              
           90.81%     
 
- --------------------------------------------------------------------------------
    
 10    TYPE OF REPORTING PERSON*     
 
           CO
 

<PAGE>
 
                                    
    CUSIP NO. 400 181 103          14D-1     
    
 1     NAME OF REPORTING PERSONS S.S OR I.R.S. IDENTIFICATION NOS. OF ABOVE
       PERSONS     
              
           NORTHROP CORPORATION     
 
- --------------------------------------------------------------------------------
    
 2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                 (a) [_]
                                                                         (b) [_]
 
- --------------------------------------------------------------------------------
    
 3     SEC USE ONLY     
 
- --------------------------------------------------------------------------------
    
 4     SOURCE OF FUNDS*     
 
           BK
 
- --------------------------------------------------------------------------------
    
 5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
       ITEM 2(e) or 2(f)                                                     [_]
 
- --------------------------------------------------------------------------------
    
 6     CITIZENSHIP OR PLACE OF ORGANIZATION     
 
           DELAWARE
 
- --------------------------------------------------------------------------------
    
 7     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     
 
           INDIRECTLY: 31,585,201         
                                       DIRECTLY: 2     
 
- --------------------------------------------------------------------------------
    
 8     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES CERTAIN SHARES*
                                                                             [_]
 
- --------------------------------------------------------------------------------
    
 9     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)     
              
           90.81%     
 
- --------------------------------------------------------------------------------
    
 10    TYPE OF REPORTING PERSON*     
 
           CO
 

<PAGE>
 
   
  This Amendment No. 11 (Final Amendment) 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,
as amended (the "Offer").     
          
  Item 6 of the Schedule 14D-1 is hereby amended by adding the following:     
   
ITEM 6. INTEREST IN SECURITIES OF THE SUBJECT COMPANY.     
   
  At 12:00 midnight, New York City Time, on April 15, 1994, the Offer expired.
Based on information provided by the Depositary, a total of 31,585,201 Shares
(or approximately 90.81% of the Shares outstanding) were properly tendered and
not withdrawn pursuant to the Offer. The Purchaser has accepted for payment,
and has notified the Depositary to promptly pay for, all such Shares at the
purchase price of $62 per Share in cash.     
   
  Pursuant to the Merger Agreement, a Special Meeting of Shareholders of the
Company is expected to be held on or about May 18, 1994, at which the
shareholders will consider and vote upon the Merger Agreement and the
transactions contemplated thereby (the "Merger Proposal"). Northrop and the
Purchaser intend to vote all Shares held by them in favor of the Merger
Proposal. It is anticipated that the Merger will be consummated shortly after
the Special Meeting of Shareholders, as a result of which the Company will
become a wholly-owned subsidiary of Northrop and each outstanding Share (other
than Shares held in the treasury of the Company and Shares held by Northrop and
its subsidiaries, which will be cancelled, and Shares as to which shareholders
shall have properly asserted dissenters' rights under the New York Business
Corporation Law) will be converted into the right to receive $62 per Share in
cash.     
 
                               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: May 3, 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