================================================================================ SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 SCHEDULE 13D Under the Securities Exchange Act of 1934 (Amendment No. 11) ------------------------------ 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 APRIL 12, 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 Sections 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. See Section 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 6 Pages) ================================================================================ ---------------------------------------- --------------------------------------- CUSIP No. 427056106 13D Page 2 of 6 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 ------------------------------- ------------------------------------------------------ NUMBER OF 7 SOLE VOTING POWER: 0 SHARES ------------- ------------------------------------------------------ BENEFICIALLY 8 SHARED VOTING POWER: 10,719,200 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): 9.91% --------------- ---------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON: CO --------------- ---------------------------------------------------------------------- ---------------------------------------- --------------------------------------- CUSIP No. 427056106 13D Page 3 of 6 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 ------------------------------- ------------------------------------------------------ NUMBER OF 7 SOLE VOTING POWER: 10,719,200 SHARES ------------- ------------------------------------------------------ BENEFICIALLY 8 SHARED VOTING POWER: 0 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): 9.91% --------------- ---------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON: CO --------------- ---------------------------------------------------------------------- ---------------------------------------- --------------------------------------- CUSIP No. 427056106 13D Page 4 of 6 Pages ---------------------------------------- --------------------------------------- --------------- ---------------------------------------------------------------------- 1 NAME OF REPORTING PERSON INTERNATIONAL SPECIALTY S.S. OR I.R.S. IDENTIFICATION NO. PRODUCTS INC. 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 ------------------------------- ------------------------------------------------------ NUMBER OF 7 SOLE VOTING POWER: 0 SHARES ------------- ------------------------------------------------------ BENEFICIALLY 8 SHARED VOTING POWER: 10,719,200 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): 9.91% --------------- ---------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON: CO --------------- ---------------------------------------------------------------------- This Amendment No. 11 ("Amendment No. 11") 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, Amendment No. 4 filed on February 20, 2001, Amendment No. 5 filed on February 28, 2001, Amendment No. 6 filed on March 7, 2001, Amendment No. 7 filed on March 9, 2001, Amendment No. 8 filed on March 12, 2001, Amendment No. 9 filed on April 4, 2001, and Amendment No. 10 filed on April 11, 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 April 12, 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 am in receipt of your letter today, and our response is already fully laid out in our proxy materials, which contain numerous facts that you insist on ignoring. While we are pleased that Hercules has "reactivated" its search for a permanent CEO, I do not recall Hercules ever reporting to its shareholders that it had deactivated the search. Are you now reporting that after almost six months there has been no progress on this front as well? I do agree with you, of course, that Hercules shareholders should not be misled, and so to prevent that from happening, I would propose that you and I have one or more discussions/debates before any interested group of Hercules shareholders, so that the Company's shareholders can fully understand our respective positions in the proxy contest. Please let me know. Sincerely, /s/ Samuel J. Heyman [The remainder of this page intentionally left blank.] 5 SIGNATURES After reasonable inquiry and to the best of their knowledge and belief, the undersigned certify that the information set forth in this Statement is true, complete and correct. Dated: April 12, 2001 ISP OPCO HOLDINGS INC. ISP INVESTMENTS INC. INTERNATIONAL SPECIALTY PRODUCTS INC. By: /s/ Susan B. Yoss -------------------------------------- Susan B. Yoss Executive Vice President and Treasurer 6