<PAGE>
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                               ----------------
 
                                 SCHEDULE 14D-1
                                
                             (AMENDMENT NO. 5)     
 
                   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. 5 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 29, 1994, Northrop received a letter from the Company, a copy of
which is attached hereto as Exhibit (c)(9) and incorporated herein by reference
in its entirety. On March 30, 1994, Northrop sent a letter to the Company, a
copy of which is attached hereto as Exhibit (c)(10) and incorporated herein by
reference in its entirety.     
       
ITEM 11. MATERIAL TO BE FILED AS EXHIBITS.
     
  (c)(9)   Letter dated March 29, 1994 from the Company to Northrop.     
     
  (c)(10)  Letter dated March 30, 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 30, 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
 

 EXHIBIT
   NO.                               DESCRIPTION
 -------                             -----------
     
  (c)(9)  Letter dated March 29, 1994 from the Company to Northrop.
                 
  (c)(10) Letter dated March 30, 1994 from Northrop to the Company.
              

                               Page 4 of 4 Pages





<PAGE>
 
                      [LETTERHEAD OF GRUMMAN CORPORATION]

                                                    March 29, 1994

Mr. Kent Kresa
Chairman, President and Chief
  Executive Officer
Northrop Corporation
1840 Century Park East
Los Angeles, California 90067

Dear Kent:

     I want to acknowledge receipt of your letter of March 28 and thought that 
it might be helpful to give you our thinking on the matters raised.

     First, I want to assure you that the Rules and Procedures for Submission 
of Proposals developed by us and simultaneously transmitted to both you and 
Martin Marietta on March 28, 1994, represent the carefully considered 
determination by Grumman and its Board of Directors that this is the appropriate
course to follow for all the reasons set forth in our March 28 letter. We very 
much hope that you and Martin Marietta will submit your "best and highest offer"
as contemplated by the Rules and Procedures and that each of you will make 
yourselves available for the weekend commencing with the submission of the bids 
at 5 p.m., New York time, on Thursday, March 31, as therein contemplated.

     We continue to be firmly of the view that the Rules and Procedures are fair
to both Northrop and Martin Marietta and are consistent with and promote a free 
and open bidding process as urged in Northrop's
 March 23 letter and are in the 
best interests of our shareholders and other constituencies as indicated in our 
March 28 letter.

<PAGE>
 
                                       2

     Under the process, your bid would be based on the "Agreement and Plan of 
Merger, dated as of March 24, 1994, among Northrop Corporation, Northrop 
Acquisition, Inc., and Grumman Corporation" ("Northrop Agreement"), as executed 
by you and transmitted by your counsel to our counsel. The Northrop Agreement 
expressly incorporates what you refer to as a "lockup fee" in two respects. 
First, the Northrop Agreement requires a representation by Grumman that Grumman
has terminated the Martin Marietta Agreement and Plan of Merger ("Martin 
Agreement") pursuant to Section 8.1(d)(ii) thereof, which section specifies that
no such termination can be effective until payment by Grumman to Martin Marietta
of the $50 million fee required by Section 8.3(b) thereof. Second, the Northrop 
Agreement, once executed by both parties, requires precisely the same $50 
million fee and expenses (for the benefit of Northrop) as does the Martin 
Agreement (for the benefit of Martin Marietta).

     Again, we feel that the Rules and Procedures set forth in our March 28
letter are the best assurance of a fair and orderly procedure, and we strongly
urge and hope that both Northrop and Martin Marietta will participate. We have
no confidence that in the absence of such Rules and Procedures the bidding would
conclude in the very near future; the submission by each bidder of its "best and
highest offer" at the earliest time so that the process can be brought to a
prompt and orderly conclusion is, we would suggest, in the best interest not
only of Grumman, its shareholders, and other constituencies, but also of the
bidders.

     So as to assure that any communications from us prior to the bid time, 
i.e., 5:00 p.m., Thursday, March 31, are communicated at the same time to 
Northrop and Martin Marietta, we are simultaneously transmitting this letter 
both to you and to Martin Marietta.

                                     Sincerely,

                                     /s/ RENSO L. CAPORALI

                                     Renso L. Caporali

RLC:lee
cc:  Mr. Norman R. Augustine,
     Chairman and Chief Executive Officer
     Martin Marietta Corporation




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

                                     March 30, 1994

Board of Directors
Grumman Corporation
1111 Stewart Avenue
Bethpage, New York 11714

Gentlemen and Mrs. Benson:

This letter is submitted in response to the letter, dated March 28, from Renso 
Caporali to Martin Marietta Corporation and Northrop Corporation.

We are unable to accept the rules and procedures set forth in Dr. Caporali's 
letter and have previously written on March 28 to express our concerns with 
them. To be fair, a bidding procedure under the circumstances must be open and 
public. Both bidders should have a reasonable opportunity to respond to each bid
by the other. Martin Marietta has had over two weeks to consider Northrop's $60 
bid; and it is not fair now to foreclose Northrop from submitting a further bid 
if Martin Marietta elects to increase its price. Further, we do not believe it 
is reasonable to request Northrop's approval of procedures that would allow 
Grumman and its advisors a period of more than three days to deal with any bids 
from Northrop or Martin Marietta, in complete secrecy, and with a commitment 
from Northrop not to increase its bid after that date. It is our hope that you 
will appreciate these concerns
 on Northrop's part.

In order to demonstrate our commitment to an open bidding process, Northrop is 
prepared to proceed immediately to increase its tender offer to $62 per share. 
This offer to increase Northrop's tender offer shall remain in effect until 
3:00 p.m. Eastern Standard Time, March 31, 1994. If Grumman has not accepted our
offer by agreeing to enter into the proposed merger agreement with Northrop by 
such time,  the offer will expire and Northrop's existing $60 tender offer 
(including Northrop's offer to enter into a merger agreement with Grumman at 
such price) shall remain in effect in accordance with its terms.










Northrop Corporation    1840 Century Park East    Los Angeles, California 90067



<PAGE>
 
Page 2

We note that, if Grumman enters into the proposed merger agreement with 
Northrop, at least with respect to any future bidding, Martin Marietta will be 
faced with exactly the same cost as Northrop in submitting any higher bid, as 
the result of the $50 plus million lockup fee.

We are prepared to participate in a bidding procedure which is open (i.e., each
bidder is informed of bids by the other), public, as well as fair in all other 
respects, upon receipt of Grumman's agreement to the following:

1.  Grumman shall receive and consider such further offers as Northrop or Martin
Marietta may choose to submit. Any such offers shall be based upon the existing
Martin Marietta agreement and plan of merger in the case of Martin Marietta, or
the form of agreement sent to Grumman by Northrop in the case of Northrop.

2.  Each of Northrop and Martin Marietta shall have the right for a period of 24
hours following receipt by it, in writing, of any increased offer by the other
to increase its own offer.

3.  Grumman shall not enter into a merger agreement with Northrop or amend its 
existing agreement with Martin Marietta until the expiration of any 24-hour 
period referred to in Paragraph 2.

4.  Any merger agreement, or amendment to the agreement and plan of 
merger, entered into by Grumman with Northrop or Martin Marietta shall be in the
form referred to in Paragraph 1. Without limiting the generality of the
foregoing, Grumman shall not enter into any agreement or take any action that
would impede or make more expensive the acquisition of Grumman by Northrop or
Martin Marietta, except: (i) for any increase in the consideration payable to
Grumman stockholders; and, (ii) except for the execution and delivery of the
merger agreement, or amended agreement and plan of merger, as contemplated
hereby.

We believe this procedure will accomplish Grumman's objective of bringing the
bidding process to a conclusion in the very near future, without sacrificing the
interest of Grumman's stockholders in receiving the highest offer for their
shares.

<PAGE>
 
Page 3

The proposal set forth above, we believe, is consistent with Grumman's 
objectives as stated in Dr. Caporali's letter of March 28 and 29, will alleviate
Northrop's concerns and will serve the best interests of Grumman's stockholders 
and other constituencies.

                                       Sincerely,

                                       /s/ KENT KRESA

                                       Kent Kresa