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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13D
                    Under the Securities Exchange Act of 1934

                                (Amendment No. 5)

                         ------------------------------

                              HERCULES INCORPORATED
                                (Name of Issuer)

COMMON STOCK, $25/48 STATED VALUE PER SHARE                   427056106
      (Title of class of securities)                        (CUSIP number)

                            RICHARD A. WEINBERG, ESQ.
                        C/O ISP MANAGEMENT COMPANY, INC.
                                 1361 ALPS ROAD
                             WAYNE, NEW JERSEY 07470
                                 (973) 628-4000
            (Name, address and telephone number of person authorized
                     to receive notices and communications)

                                 WITH A COPY TO:

                             STEPHEN E. JACOBS, ESQ.
                           WEIL, GOTSHAL & MANGES LLP
                                767 FIFTH AVENUE
                          NEW YORK, NEW YORK 10153-0119
                                 (212) 310-8000

                                FEBRUARY 28, 2001
             (Date of event which requires filing of this statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of ss.ss. 240.13d-1(e), 240.13d-1(f) or 240.13d-(g), check the
following box. [ ]

Note: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. Seess. 240.13d-7 for other
parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purposes of Section 18 of the Securities Exchange Act of
1934 (the "Act") or otherwise subject to the liabilities of that section of the
Act but shall be subject to all other provisions of the Act. (However, see the
Notes.)

                         (Continued on following pages)

                               (Page 1 of 7 Pages)


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NY2:\1019821\01\L%WD01!.DOC\54104.0018



-----------------------------------------------------------              --------------------------------------------------------
                                                                                                         
CUSIP No. 427056106                                             13D                                            Page 2 of 7 Pages
-----------------------------------------------------------              --------------------------------------------------------

----------------------    -------------------------------------------------------------------------------------------------------
          1               NAME OF REPORTING PERSON                                ISP OPCO HOLDINGS INC.
                          S.S. OR I.R.S. IDENTIFICATION NO.
                          OF ABOVE PERSON
----------------------    -------------------------------------------------------------------------------------------------------
          2               CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                    (a) [ ]
                                                                                                               (b) [X]
----------------------    -------------------------------------------------------------------------------------------------------
          3               SEC USE ONLY
----------------------    -------------------------------------------------------------------------------------------------------
          4               SOURCE OF FUNDS:                                                  OO
----------------------    -------------------------------------------------------------------------------------------------------
          5               CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
                          PURSUANT TO ITEM 2(d) OR 2(e):                                                            [ ]
----------------------    -------------------------------------------------------------------------------------------------------
          6               CITIZENSHIP OR PLACE OF ORGANIZATION:                                              Delaware
----------------------    -------------------------------------------------------------------------------------------------------
                                  7               SOLE VOTING POWER:                                                  0
      NUMBER OF
        SHARES            -------------------     -------------------------------------------------------------------------------
                                  8               SHARED VOTING POWER:                                       10,719,200
     BENEFICIALLY
       OWNED BY
                          -------------------     -------------------------------------------------------------------------------
         EACH                     9               SOLE DISPOSITIVE POWER:                                             0
      REPORTING

     PERSON WITH          -------------------     -------------------------------------------------------------------------------
                                  10              SHARED DISPOSITIVE POWER:                                  10,719,200

----------------------    -------------------------------------------------------------------------------------------------------
         11               AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:                           10,719,200
----------------------    -------------------------------------------------------------------------------------------------------
         12               CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                         [ ]
----------------------    -------------------------------------------------------------------------------------------------------
         13               PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):                                           9.98%
----------------------    -------------------------------------------------------------------------------------------------------
         14               TYPE OF REPORTING PERSON:                               CO
----------------------    -------------------------------------------------------------------------------------------------------




-----------------------------------------------------------              --------------------------------------------------------
CUSIP No. 427056106                                             13D                                            Page 3 of 7 Pages
-----------------------------------------------------------              --------------------------------------------------------

----------------------    -------------------------------------------------------------------------------------------------------
          1               NAME OF REPORTING PERSON                                ISP INVESTMENTS INC.
                          S.S. OR I.R.S. IDENTIFICATION NO.
                          OF ABOVE PERSON
----------------------    -------------------------------------------------------------------------------------------------------
          2               CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                    (a) [ ]
                                                                                                               (b) [X]
----------------------    -------------------------------------------------------------------------------------------------------
          3               SEC USE ONLY
----------------------    -------------------------------------------------------------------------------------------------------
          4               SOURCE OF FUNDS:                                                  WC, OO
----------------------    -------------------------------------------------------------------------------------------------------
          5               CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
                          PURSUANT TO ITEM 2(d) OR 2(e):                                                           [ ]
----------------------    -------------------------------------------------------------------------------------------------------
          6               CITIZENSHIP OR PLACE OF ORGANIZATION:                                              Delaware
----------------------    -------------------------------------------------------------------------------------------------------
                                  7               SOLE VOTING POWER:                                         10,719,200
      NUMBER OF
        SHARES            -------------------     -------------------------------------------------------------------------------
                                  8               SHARED VOTING POWER:                                                0
     BENEFICIALLY
       OWNED BY
                          -------------------     -------------------------------------------------------------------------------
         EACH                     9               SOLE DISPOSITIVE POWER:                                    10,719,200
      REPORTING

     PERSON WITH          -------------------     -------------------------------------------------------------------------------
                                  10              SHARED DISPOSITIVE POWER:                                           0

----------------------    -------------------------------------------------------------------------------------------------------
         11               AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:                           10,719,200
----------------------    -------------------------------------------------------------------------------------------------------
         12               CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                        [ ]
----------------------    -------------------------------------------------------------------------------------------------------
         13               PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):                                           9.98%
----------------------    -------------------------------------------------------------------------------------------------------
         14               TYPE OF REPORTING PERSON:                               CO
----------------------    -------------------------------------------------------------------------------------------------------



-----------------------------------------------------------              --------------------------------------------------------
CUSIP No. 427056106                                             13D                                            Page 4 of 7 Pages
-----------------------------------------------------------              --------------------------------------------------------

----------------------    -------------------------------------------------------------------------------------------------------
          1               NAME OF REPORTING PERSON                                INTERNATIONAL SPECIALTY PRODUCTS INC.
                          S.S. OR I.R.S. IDENTIFICATION NO.
                          OF ABOVE PERSON
----------------------    -------------------------------------------------------------------------------------------------------
          2               CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:                                    (a) [ ]
                                                                                                               (b) [X]
----------------------    -------------------------------------------------------------------------------------------------------
          3               SEC USE ONLY
----------------------    -------------------------------------------------------------------------------------------------------
          4               SOURCE OF FUNDS:                                                  OO
----------------------    -------------------------------------------------------------------------------------------------------
          5               CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
                          PURSUANT TO ITEM 2(d) OR 2(e):                                                            [ ]
----------------------    -------------------------------------------------------------------------------------------------------
          6               CITIZENSHIP OR PLACE OF ORGANIZATION:                                              Delaware
----------------------    -------------------------------------------------------------------------------------------------------
                                  7               SOLE VOTING POWER:                                                  0
      NUMBER OF
        SHARES            -------------------     -------------------------------------------------------------------------------
                                  8               SHARED VOTING POWER:                                       10,719,200
     BENEFICIALLY
       OWNED BY
                          -------------------     -------------------------------------------------------------------------------
         EACH                     9               SOLE DISPOSITIVE POWER:                                             0
      REPORTING

     PERSON WITH          -------------------     -------------------------------------------------------------------------------
                                  10              SHARED DISPOSITIVE POWER:                                  10,719,200

----------------------    -------------------------------------------------------------------------------------------------------
         11               AGGREGATE AMOUNT BENEFICIALLY OWNED BY REPORTING PERSON:                           10,719,200
----------------------    -------------------------------------------------------------------------------------------------------
         12               CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES:                        [ ]
----------------------    -------------------------------------------------------------------------------------------------------
         13               PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11):                                           9.98%
----------------------    -------------------------------------------------------------------------------------------------------
         14               TYPE OF REPORTING PERSON:                               CO
----------------------    -------------------------------------------------------------------------------------------------------





                  This Amendment No. 5 ("Amendment No. 5") amends the statement
of beneficial ownership on Schedule 13D ("Schedule 13D") filed on July 24, 2000,
as amended by Amendment No. 1 filed on October 11, 2000, Amendment No. 2 filed
on January 23, 2001, Amendment No. 3 filed on February 7, 2001 and Amendment No.
4 filed on February 20, 2001, by and on behalf of ISP Opco Holdings Inc. ("ISP
Opco"), ISP Investments Inc. ("ISP Investments"), and International Specialty
Products Inc. ("ISP" and together with ISP Investments and ISP Opco, the
"Reporting Persons") with respect to their ownership of common stock, stated
value $25/48 per share ("Common Stock"), of Hercules Incorporated (the
"Company"). Capitalized terms used herein and not defined herein have the
meanings ascribed thereto in the Schedule 13D, as previously amended.

ITEM 4.           PURPOSE OF TRANSACTION

                  On February 28, 2001, Samuel J. Heyman, Chairman of the Board
of ISP, sent the following letter to Mr. Thomas Gossage, Chairman, CEO and
President of the Company:

Mr. Thomas Gossage
Chairman, CEO and President
Hercules Incorporated
Hercules Plaza
1313 North Market Street
Wilmington, Delaware 19894-0001

Dear Tom:

                  I was disappointed in your February 23rd letter and your
Board's decision to reject ISP's compromise proposal. Contrary to your apparent
belief, there is nothing inconsistent in our view with a shareholder being
permitted to underscore its confidence in the underlying values of the Company
by making an additional investment on the one hand and your "on going sale
process" on the other.

                  We are concerned with what seems to us Hercules' narrow,
one-dimensional approach to maximizing shareholder values. If Hercules is unable
to sell the Company on an advantageous basis, it will have needlessly deprived
Hercules shareholders of the opportunity to decide for themselves whether to
accept our previously proposed $17 1/2 tender offer or, under our compromise
approach, sell their shares in the open market to ISP or any other shareholder
wishing to acquire up to 20% of the Company's shares. This position is
especially surprising given the multitude of takeover defenses the Company has
erected and the fact that we have always been willing to address any of your
legitimate concerns in the form of reasonable conditions with respect to our
ownership position.

                  With respect to your reference to the withdrawal of our
proposed tender offer, as you know, the October offer expired by its own terms
on account of the fact that your Board had refused to exempt it from its poison
pill and related Delaware statutory provisions. That is why we put forward the
compromise proposal to permit ISP to acquire up to 20% of Hercules' shares
rather than 35%. While we can only assume that if your Board is unwilling to
permit our acquisition of up to 20% of Hercules shares, it would not have gone


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along with our 35% proposal either - but if we are missing something in this
regard, please let us know.

                  With regard to the last point in your letter, your claim that
ISP's actions/statements are a hindrance to your efforts is sheer nonsense, as
in point of fact we have been very patient and constructive shareholders for
some time now. As you will recall, it was ISP who first encouraged Hercules to
abandon its flawed restructuring strategy and sell the Company. While it took
Hercules quite some time to adopt this strategy, we not only applauded the
decision but have provided assurances, whether we were a 10%, 20%, or 35% owner,
that we would support the sale of the Company at a fair price. In fact, despite
your invitation, we have refrained from taking part in the auction process in
large measure because we view our Hercules stake as an investment and so that
there could be no claim that our participation, as the Company's major
shareholder, would have a chilling effect on other interested bidders.

                  Tom, you know that we have a high conviction concerning the
way in which Hercules has conducted the Company's affairs in recent years. In
this connection, we intend to bring these matters to the attention of Hercules
shareholders at the Company's upcoming Annual Meeting. Moreover, as owners of
more than 10.7 million Hercules shares, we will be seeking to elect a slate of
directors, with a strong ownership orientation committed to the interests of
Hercules shareholders, to replace the four incumbent directors up for
re-election this year, who we understand (as of the last public filing) own in
the aggregate less than 50,000 shares.

                                   Sincerely,

                                   /s/ Samuel J. Heyman

                                      * * *

         ISP INTENDS TO FILE A PRELIMINARY PROXY STATEMENT WITH THE U.S.
         SECURITIES AND EXCHANGE COMMISSION RELATING TO ISP'S SOLICITATION OF
         PROXIES FROM THE STOCKHOLDERS OF THE COMPANY FOR USE AT THE 2001 ANNUAL
         MEETING. ISP STRONGLY ADVISES ALL HERCULES STOCKHOLDERS TO READ THE
         PROXY STATEMENT WHEN IT IS AVAILABLE BECAUSE IT WILL CONTAIN IMPORTANT
         INFORMATION. INFORMATION RELATING TO THE PARTICIPANTS IN ISP'S PROXY
         SOLICITATION IS CONTAINED IN THE SOLICITING MATERIAL UNDER RULE 14a-12
         FILED BY ISP WITH THE SEC ON FEBRUARY 7, 2001. INVESTORS CAN GET ISP'S
         PROXY STATEMENT WHEN IT IS AVAILABLE AND OTHER RELEVANT DOCUMENTS AT NO
         CHARGE ON THE SEC WEBSITE AT HTTP:\\WWW.SEC.GOV.


             [The remainder of this page intentionally left blank.]





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                                   SIGNATURES

                  After reasonable inquiry and to the best of their knowledge
and belief, the undersigned certifies that the information set forth in this
Statement is true, complete and correct.

Dated: February 28, 2001

                            ISP OPCO HOLDINGS INC.
                            ISP INVESTMENTS INC.
                            INTERNATIONAL SPECIALTY PRODUCTS INC.


                            By: /s/ Richard A. Weinberg
                                -----------------------------------------------
                                Richard A. Weinberg
                                Executive Vice President, General Counsel and
                                Secretary
















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