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SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

SCHEDULE 13D

[Rule 13d-101]

INFORMATION TO BE INCLUDED IN STATEMENTS FILED

PURSUANT TO § 240.13d-1(a) AND AMENDMENTS

THERETO FILED PURSUANT TO § 240.13d-2(a)

Amendment No. 20

Navistar International Corporation

(Name of Issuer)

Common Stock, par value $0.10 per share

(Title of Class of Securities)

63934E108

(CUSIP Number)

Janet Yeung

MHR Fund Management LLC

1345 Avenue of the Americas, 42^nd Floor

New York, New York 10105

(212) 262-0005

(Name, Address and Telephone Number of Person Authorized to Receive Notices of Communication)

April 17, 2018

(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 §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(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 §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose 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).

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Explanatory Note

This statement on Schedule 13D (this “Statement”) amends and supplements, as Amendment No. 20, the Schedule 13D filed on June 15, 2012 (the “Initial Schedule 13D”), which was amended on June 25, 2012 by Amendment No. 1 to the Initial Schedule 13D (“Amendment No. 1”), on July 10, 2012 by Amendment No. 2 to the Initial Schedule 13D (“Amendment No. 2”), on October 9, 2012 by Amendment No. 3 to the Initial Schedule 13D (“Amendment No. 3”), on October 26, 2012 by Amendment No. 4 to the Initial Schedule 13D (“Amendment No. 4”), on December 12, 2012 by Amendment No. 5 to the Initial Schedule 13D (“Amendment No. 5”), on July 15, 2013 by Amendment No. 6 to the Initial Schedule 13D (“Amendment No. 6”), on July 17, 2013 by Amendment No. 7 to the Initial Schedule 13D (“Amendment No. 7”), on March 11, 2014 by Amendment No. 8 to the Initial Schedule 13D (“Amendment No. 8”), on April 11, 2014 by Amendment No. 9 to the Initial Schedule 13D (“Amendment No. 9”), on June 24, 2015 by Amendment No. 10 to the Initial Schedule 13D (“Amendment No. 10”), on December 18, 2014 by Amendment No. 11 to the Initial Schedule 13D (“Amendment No. 11”), on January 30, 2015 by Amendment No. 12 to the Initial Schedule 13D (“Amendment No. 12”), on June 11, 2015 by Amendment No. 13 to the Initial Schedule 13D (“Amendment No. 13”), on July 27, 2015 by Amendment No. 14 to the Initial Schedule 13D (“Amendment No. 14”), on September 4, 2015 by Amendment No. 15 to the Schedule 13D (“Amendment No. 15”), on December 18, 2015 by Amendment No. 16 to the Initial Schedule 13D (“Amendment No. 16”), on September 6, 2016 by Amendment No. 17 to the Initial Schedule 13D (“Amendment No. 17”), on September 21, 2016 by Amendment No. 18 to the Initial Schedule 13D (“Amendment No. 18”) and on March 3, 2017 by Amendment No. 19 to the Initial Schedule 13D (“Amendment No. 19” and together with Amendment No. 1 through Amendment No. 18 and the Initial Schedule 13D, the “Schedule 13D”), and relates to shares of common stock, par value $0.10 per share (the “Common Stock”), of Navistar International Corporation (the “Issuer”). Except as otherwise provided, capitalized terms used in this Statement but not defined herein shall have the respective meanings given to such terms in Amendment No. 19.

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Item 4. Purpose of Transaction.

Item 4 is hereby amended by adding the following:

Pursuant to the Settlement Agreement Amendment (as defined in Amendment No. 6), MHR (as defined in Amendment No. 6) has designated Raymond Miller as the Second MHR Nominee (as defined in Amendment No. 6) to serve on the Board. Mr. Miller is a Principal at MHR Fund Management LLC. The Board elected Mr. Miller effective April 17, 2018. In addition, Mr. Miller was appointed to the Issuer’s Audit Committee and Compensation Committee. Mr. Miller replaces Michael Sirignano, who resigned as a director of the Company effective upon the acceptance by the Board of his notice of resignation, which occurred at the same meeting of the Board in which Mr. Miller was elected.

Item 5. Interests in Securities of the Issuer.

Item 5(a)(ix), Item 5(b)(ix) and Item 5(c) are hereby amended by deleting such items in their entirety and replacing them with the following:

The percentages set forth below are based on 98,689,315 shares of Common Stock outstanding as of February 28, 2018, as disclosed by the Issuer on its Quarterly Report on Form 10-Q filed on March 8, 2018.

(a) (ix) Dr. Rachesky may be deemed to be the beneficial owner of 16,281,256 shares of Common Stock (approximately 16.5% of the total number of shares of Common Stock outstanding, calculated in accordance with Rule 13d–3(d)(1)(i) under the Act). This number consists of (A) all of the shares of Common Stock otherwise described in this Item 5 by virtue of Dr. Rachesky’s position as the managing member of each of MHRC, Institutional Advisors III and MHR Holdings, (B) 25,934 shares of Common Stock held directly, (C) 30,000 shares of Common Stock that can be obtained upon the exercise of certain stock options and (D) 322.623 phantom stock units convertible into Common Stock upon settlement.

(b) (ix) Dr. Rachesky may be deemed to have (x) the sole power to direct the disposition of 16,281,256 shares of Common Stock which may be deemed to be beneficially owned by Dr. Rachesky as described above, and (y) the sole power to direct the voting of 16,281,256 shares of Common Stock which may be deemed to be beneficially owned by Dr. Rachesky as described above.

(c) On February 28, 2018, 3,086.554 phantom stock units held by Dr. Rachesky were settled for 3,086 shares of Common Stock (and a cash reimbursement for the fractional phantom stock unit). On April 1, 2018, Dr. Rachesky was granted (i) 571 shares of Common Stock and (ii) 322.623 phantom stock units convertible into Common Stock upon settlement.

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SIGNATURES

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

Dated: April 18, 2018

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