SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO RULES 13d-1(a) AND AMENDMENTS THERETO FILED

PURSUANT TO RULE 13d-2(a)

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 2)*

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 Rule 13d-1(e), 13d-1(f) or 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 Rule 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 purpose of Section 18 of the Securities Exchange Act of 1934 (“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).

AMENDMENT NO. 2 TO SCHEDULE 13D

Introduction

This Amendment No. 2 to Schedule 13D (this “Amendment”) is being filed with the Securities and Exchange Commission (the “SEC”) on behalf of (i) Neil S. Subin; (ii) MILFAM LLC; (iii) Milfam Investments LLC (“MINVEST”); (iv) MILFAM CI LLC SPARTACUS; and (v) MILFAM CI Management LLC (each person and entity named in items (i) through (v), collectively, the “Reporting Persons”). This Amendment amends and supplements the original Schedule 13D filed by the Reporting Persons with the SEC on October 29, 2020, as amended by the Schedule 13D/A previously filed on November 6, 2020 (collectively, the “Schedule 13D”).

Capitalized terms used but not otherwise defined in this Amendment have the meanings ascribed to such terms in the Schedule 13D. Except as expressly amended and supplemented by this Amendment, the Schedule 13D is not amended or supplemented in any respect, and the disclosures set forth in the Schedule 13D, other than as amended herein are incorporated by reference herein.

Item 4. Purpose of the Transaction

Item 4 is hereby amended and modified to include the following:

As previously announced by Spartacus Acquisition Corporation (the “Issuer” or the “Company”), on June 9, 2021, the Issuer entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Spartacus Acquisition Shelf Corp., a Delaware corporation (“Shelf”), NextNav, LLC, a Delaware limited liability company, NextNav Holdings, LLC, a Delaware limited liability company (“Holdings”), NEA 14 NextNav Blocker, LLC, a Delaware limited liability company (“NEA Blocker”), Oak NextNav Blocker, LLC, a Delaware limited liability company (“Oak Blocker”), Columbia Progeny Partners IV, Inc., a Delaware corporation (“Columbia Blocker”), Global Long Short Partners Aggregating Holdings Del VII LLC, a Delaware limited liability company (“GS Blocker 1”), Global Private Opportunities Partners Holdings II Corp., a Delaware corporation, (“GS Blocker 2,” and collectively with NEA Blocker, Oak Blocker, Columbia Blocker, and GS Blocker 1, the “Blockers”), SASC (SPAC) Merger Sub 1 Corporation, a Delaware corporation (“MS 1”), SASC (Target) Merger Sub 2 LLC, a Delaware limited liability company (“MS 2”), SASC (NB) Merger Sub 3 LLC, a Delaware limited liability company (“MS 3”), SASC (OB) Merger Sub 4 LLC, a Delaware limited liability company (“MS 4”), SASC (CB) Merger Sub 5 Corporation, a Delaware corporation (“MS 5”), SASC (GB1) Merger Sub 6 LLC, a Delaware limited liability company (“MS 6”) , and SASC (GB2) Merger Sub 7 Corporation, a Delaware corporation (“MS 7,” and collectively with MS 1, MS 2, MS 3, MS 4, MS 5, and MS 6, the “Merger Entities”). The Merger Entities are each wholly owned subsidiaries of Shelf. The Merger Agreement provides for, among other things, (a) MS 1 to be merged with and into the Company, with the Company surviving the merger; (b) MS 2 to be merged with and into Holdings, with Holdings surviving the merger; (c) MS 3 to be merged with and into NEA Blocker, with NEA Blocker surviving the merger; (d) MS 4 to be merged with and into Oak Blocker, with Oak Blocker surviving the merger; (e) MS 5 to be merged with and into Columbia Blocker, with Columbia Blocker surviving the merger; (f) MS 6 to be merged with and into GS Blocker 1, with GS Blocker 1 surviving the merger; and (g) MS 7 to be merged with and into GS Blocker 2, with GS Blocker 2 surviving the merger.

As a result of the transactions contemplated in the Merger Agreement (collectively, the “Transactions”), the Company, NEA Blocker, Oak Blocker, Columbia Blocker, GS Blocker 1, GS Blocker 2 and Holdings and the various operating subsidiaries of Holdings, will become wholly owned subsidiaries of Shelf, and the Company’s stockholders, the equity holders of each of NEA Blocker, Oak Blocker, Columbia Blocker, GS Blocker 1, GS Blocker 2, and the equity holders of Holdings, will become stockholders of Shelf.

Concurrently with the execution and delivery of the Merger Agreement, certain “qualified institutional buyers” (as defined in Rule 144A under the Securities Act of 1933, as amended (the “Securities Act”)) or institutional “accredited investors” (as such term is defined in Rule 501 under the Securities Act) (including MINVEST) (collectively, the “PIPE Investors”), entered into subscription agreements (the “PIPE Subscription Agreements”) pursuant to which the PIPE Investors have committed to subscribe for and purchase up to 20.5 million shares of Company Class A common stock (the “PIPE Shares”) at a purchase price per share of $10.00 for aggregate gross proceeds of $205 million (the “PIPE Investment”). The purchase of the PIPE Shares will be consummated immediately prior to the closing, with such PIPE Shares immediately being cancelled in connection with the mergers and in consideration for newly issued Shelf common stock.

MINVEST, one of the Reporting Persons, subscribed to purchase 1,105,000 PIPE Shares pursuant to a PIPE Subscription Agreement.

The closing of the PIPE Investment is contingent upon, among other things, the substantially concurrent consummation of the Transactions. Accordingly, the Reporting Persons are not deemed to have the right to acquire the PIPE Shares at this time and are not “beneficial owners” as such term is defined in Rule 13d-3 under the Act, of the PIPE Shares until the material conditions to the PIPE Subscription Agreements are met.

The foregoing descriptions of the Merger Agreement, and the PIPE Subscription Agreements and the transactions contemplated thereby do not purport to be complete and are qualified in their entirety by reference to the Merger Agreement, which is filed as Exhibit 2.1 to the Form 8-K filed by the Issuer with the SEC on June 10, 2021 (the “Form 8-K”) and the Subscription Agreements, a form of which is filed as Exhibit 10.2 to the Form 8-K and each of the foregoing is incorporated herein by reference.

Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer.

The information contained in Item 6 of the Schedule 13D is hereby amended and supplemented by adding the following thereto:

The additional information furnished in Item 4 of this Amendment is incorporated into this Item 6 by reference.

Item 7. Materials to be Filed as Exhibits:

SIGNATURE

After reasonable 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: June 30, 2021