EXECUTION VERSION REGISTRATION RIGHTS AGREEMENT THIS REGISTRATION RIGHTS AGREEMENT (this “Agreement”), dated as of February 6, 2026, is made by and between MASTER INVESTMENT GROUP, a a family office organized under the laws of Ras Al Khaima, UAE (the “Investor”), and NAUTICUS ROBOTICS, INC., a company incorporated under the laws of the State of Delaware (the “Company”). The Investor and the Company may be referred to herein individually as a “Party” and collectively as the “Parties”. WHEREAS, the Company and the Investor have entered into that certain Securities Purchase Agreement, dated as of February 6, 2026 (the “Purchase Agreement”), pursuant to which the Company would issue to the Investor certain shares of Series D Convertible Preferred Stock (the “Preferred Stock”) and certain common stock purchase warrants (the “Warrants”) ; and WHEREAS, pursuant to the terms of, and in consideration for the Investor entering into, the Purchase Agreement, and to induce the Investor to execute and deliver the Purchase Agreement, the Company has agreed to provide the Investor with certain registration rights under the Securities Act of 1933, as amended, and the rules and regulations thereunder, or any similar successor statute (collectively, the “Securities Act”). AGREEMENT NOW, THEREFORE, in consideration of the premises and the mutual covenants contained herein and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Company and the Investor hereby agree as follows: 1. DEFINITIONS. Capitalized terms used herein and not otherwise defined herein shall have the respective meanings set forth in the Purchase Agreement. As used in this Agreement, the following terms shall have the following meanings: (a) “Agreement” shall have the meaning set forth in the Recitals. (b) “Business Day” means any day except Saturday, Sunday and any day which shall be a federal legal holiday in the United States or a day on which the Federal Reserve Bank of New York is closed and/or any of the following exchanges on which the Common Stock is traded and listed, or any successor(s) thereto, is not open for at least five (5) hours of trading: the Nasdaq Capital Market; the Nasdaq Global Market; the Nasdaq Global Select Market, the New York Stock Exchange; or the NYSE American; and any successor to any of the foregoing markets or exchanges. (c) “Common Shares” means (x) the Company’s shares of common stock, $0.0001 par value per share, and (y) any capital stock into which such common stock shall have been changed or any share capital resulting from a reclassification of such common stock. (d) “Company” shall have the meaning set forth in the Recitals. (e) “Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder. (f) “Investor” shall have the meaning set forth in the Recitals. (g) “Person” means a corporation, a limited liability company, an association, a partnership (whether general or limited), an organization, a business, an individual, a governmental or political subdivision, or a governmental agency. (h) “Preferred Stock” has the meaning set forth in the Recitals. (i) “Prospectus” means the prospectus included in a Registration Statement (including, without limitation, a prospectus that includes any information previously omitted from a prospectus filed as part of an effective registration statement in reliance upon Rule 430A promulgated under the Securities Act), as amended or supplemented by any prospectus supplement, with respect to the terms of the offering of any portion of the Registrable Securities


 
2 covered by a Registration Statement, and all other amendments and supplements to the Prospectus, including post- effective amendments, and all material incorporated by reference or deemed to be incorporated by reference in such Prospectus. (j) “Purchase Agreement” shall have the meaning set forth in the Recitals. (k) “Registrable Securities” means all of (i) the Common Shares issuable upon conversion of the Preferred Stock and upon the exercise of the Warrants, and (ii) any shares of capital stock issued or issuable with respect to the Common Shares, including, without limitation, (1) as a result of any stock split, stock dividend, or other distribution, recapitalization, or similar event, or otherwise, and (2) shares of capital stock of the Company into which the Common Shares are converted or exchanged and shares of capital stock of a successor entity into which the Common Shares are converted or exchanged. As to any particular Registrable Securities, such securities shall cease to be Registrable Securities when (i) the SEC has declared a Registration Statement covering such securities effective and such securities have been disposed of pursuant to such effective Registration Statement, (ii) such securities are sold under circumstances in which all of the applicable conditions of Rule 144 under the Securities Act are met, or (iii) such securities have ceased to be outstanding. (l) “Registration Statement” means any registration statement of the Company filed pursuant to this Agreement, including the Prospectus, amendments and supplements to such registration statement or Prospectus, including post-effective amendments, all exhibits thereto, and all material incorporated by reference or deemed to be incorporated by reference in such registration statement. (m) “Rule 144” means Rule 144 under the Securities Act or any successor rule thereto. (n) “SEC” means the Securities and Exchange Commission or any other federal agency administering the Securities Act and the Exchange Act at the time. (o) “Securities Act” shall have the meaning set forth in the Recitals. (p) “Selling Expenses” means all underwriting discounts, selling commissions, and stock transfer taxes applicable to the sale of Registrable Securities. (q) “Warrants” shall have the meaning set forth in the Recitals.. 2. REGISTRATION. (a) Whenever the Company proposes to file a new Registration Statement to register the offer and sale of any shares of its Common Shares under the Securities Act for an offering to be made on a delayed or continuous basis pursuant to Rule 415 under the Securities Act or any successor rule thereto (other than a registration (i) pursuant to a Registration Statement on Form S-8 (or other registration solely relating to an offering or sale to employees or directors of the Company pursuant to any employee stock plan or other employee benefit arrangement), (ii) pursuant to a Registration Statement on Form S-4 (or similar form that relates to a transaction subject to Rule 145 under the Securities Act or any successor rule thereto), or (iii) in connection with any dividend or distribution reinvestment or similar plan), whether for its own account or for the account of one or more stockholders of the Company, and the form of Registration Statement to be used may be used for any registration of the offer and sale of Registrable Securities, the Company shall give written notice no later than five (5) Business Days prior to the filing of such Registration Statement to the Investor of its intention to effect such a registration and shall include in such Registration Statement all Registrable Securities with respect to which the Company has received written requests for inclusion from the Investor within three (3) Business Days after the Company’s notice has been given to the Investor. The Company may postpone or withdraw the filing or the effectiveness of a Registration Statement at any time in its sole discretion. 3. RELATED OBLIGATIONS. (a) The Company shall, not less than three (3) Business Days prior to the filing of each Registration Statement and not less than one Business Day prior to the filing of any related amendments and supplements to all Registration Statements (except for Annual Reports on Form 10-K, supplements and amendments to update the Registration Statement solely for information reflected in the Company’s Annual Reports on Form 10-K, Quarterly


 
3 Reports on Form 10-Q, or Current Reports on Form 8-K), furnish to the Investor copies of all such documents proposed to be filed, which documents (other than those incorporated or deemed to be incorporated by reference) will be subject to the reasonable and prompt review of the Investor. The Company shall not file a Registration Statement or any such Prospectus or any amendments or supplements thereto to which the Investor shall reasonably object in good faith. (b) If requested by the Investor, the Company shall furnish to the Investor, without charge (i) one copy (which may be in electronic form) of such Registration Statement as declared effective by the SEC and any amendment(s) thereto, including financial statements and schedules, all documents incorporated therein by reference, all exhibits and each preliminary prospectus, and (ii) one copy (which may be in electronic form) of the final prospectus included in such Registration Statement and all amendments and supplements thereto. (c) The Company shall use its commercially reasonable efforts to (i) register and qualify the Registrable Securities covered by a Registration Statement under such other securities or “blue sky” laws of such jurisdictions in the United States as the Investor reasonably requests, , and (ii) take all other actions reasonably necessary or advisable to qualify the Registrable Securities for sale in such jurisdictions; provided, however, that the Company shall not be required in connection therewith or as a condition thereto to (w) make any change to its articles of incorporation or bylaws, (x) qualify to do business in any jurisdiction where it would not otherwise be required to qualify but for this Section 3(c), (y) subject itself to general taxation in any such jurisdiction, or (z) file a general consent to service of process in any such jurisdiction. The Company shall promptly notify the Investor of the receipt by the Company of any notification with respect to the suspension of the registration or qualification of any of the Registrable Securities for sale under the securities or “blue sky” laws of any jurisdiction in the United States or its receipt of actual notice of the initiation or threat of any proceeding for such purpose. (d) The Company shall promptly notify the Investor in writing (i) when a Prospectus or any Prospectus supplement or post-effective amendment has been filed, and when a Registration Statement or any post-effective amendment has become effective (notification of such effectiveness shall be delivered to the Investor by email on the same day of such effectiveness), (ii) of any request by the SEC for amendments or supplements to a Registration Statement or related prospectus or related information, and (iii) of the Company’s reasonable determination that a post-effective amendment to a Registration Statement would be appropriate. The Company shall respond as promptly as reasonably practicable to any comments received from the SEC with respect to a Registration Statement or any amendment thereto. (e) The Company shall use its commercially reasonable efforts to prevent the issuance of any stop order or other suspension of effectiveness of a Registration Statement, or the suspension of the qualification of any of the Registrable Securities for sale in any jurisdiction within the United States of America and, if such an order or suspension is issued, to promptly obtain the withdrawal of such order or suspension and to notify the Investor of the issuance of such order and the resolution thereof or its receipt of actual notice of the initiation or threat of any proceeding for such purpose. (f) Without limiting any obligation of the Company under the Purchase Agreement, the Company shall use commercially reasonable efforts to cause all of the Registrable Securities covered by each Registration Statement to be listed on the Principal Market. The Company shall pay all fees and expenses in connection with satisfying its obligation under this Section 3(f). (g) The Company shall hold in confidence and not make any disclosure of information concerning the Investor provided to the Company unless (i) disclosure of such information is necessary to comply with federal or state securities laws, (ii) the disclosure of such information is necessary to avoid or correct a misstatement or omission in any Registration Statement, (iii) the release of such information is ordered pursuant to a subpoena or other final, non-appealable order from a court or governmental body of competent jurisdiction, or (iv) such information has been made generally available to the public other than by disclosure in violation of this Agreement or any other agreement. The Company agrees that it shall, upon learning that disclosure of such information concerning the Investor is sought in or by a court or governmental body of competent jurisdiction or through other means, give prompt written notice to such Investor if not prohibited by applicable law and allow such Investor, at the Investor’s expense, to undertake appropriate action to prevent disclosure of, or to obtain a protective order for, such information. (h) The Company shall cooperate with the Investor to facilitate the timely preparation and delivery of certificates representing the Registrable Securities to be sold pursuant to such Registration Statement or Rule 144 and representing such number of Common Shares and registered in such names as the Investor may reasonably request a


 
4 reasonable period of time prior to sales of Registrable Securities pursuant to such Registration Statement or Rule; provided, that the Company may satisfy its obligations hereunder without issuing physical stock certificates through the issuance of the Registrable Securities in book entry form. 4. OBLIGATIONS OF THE INVESTOR. (a) The Investor covenants and agrees that it will comply with the prospectus delivery requirements of the Securities Act as applicable to it or an exemption therefrom in connection with sales of Registrable Securities pursuant to any Registration Statement. (b) The Investor, by its acceptance of the Registrable Securities, agrees to cooperate with the Company as reasonably requested by the Company in connection with the preparation and filing of each Registration Statement hereunder, unless the Investor has notified the Company in writing of the Investor’s election to exclude all of the Investor’s Registrable Securities from such Registration Statement. 5. EXPENSES OF REGISTRATION. All expenses incurred by the Company in complying with its obligations pursuant to this Agreement and in connection with the registration and disposition of Registrable Securities shall be paid by the Company, including, without limitation, all registration, listing, and qualifications fees, printers, fees and expenses of the Company's counsel and accountants (excluding any Selling Expenses and any legal fees of the Investor’s counsel associated with the review of each Registration Statement). 6. INDEMNIFICATION. With respect to Registrable Securities which are included in a Registration Statement under this Agreement: (a) To the fullest extent permitted by law, the Company will, and hereby does, indemnify, hold harmless, and defend the Investor, its directors, and officers (each, an “Indemnified Person”), against any losses, claims, damages, liabilities, judgments, fines, penalties, charges, costs, reasonable attorneys’ fees, amounts paid in settlement, or expenses (collectively, “Claims”) incurred in investigating, preparing, or defending any action, claim, suit, inquiry, proceeding, investigation, or appeal taken from the foregoing by or before any court or governmental, administrative, or other regulatory agency, body, or the SEC, whether pending or threatened, whether or not an Indemnified Party is or may be a party thereto (“Indemnified Damages”), to which any of them may become subject insofar as such Claims (or actions or proceedings, whether commenced or threatened, in respect thereof) arise out of or are based upon: (i) any untrue statement or alleged untrue statement of a material fact in a Registration Statement or any post-effective amendment thereto or in any filing made in connection with the qualification of the offering under the securities or other “blue sky” laws of any jurisdiction in which Registrable Securities are offered (“Blue Sky Filing”), or the omission or alleged omission to state a material fact required to be stated therein or necessary to make the statements therein not misleading; (ii) any untrue statement or alleged untrue statement of a material fact contained in any final prospectus (as amended or supplemented, if the Company files any amendment thereof or supplement thereto with the SEC) or the omission or alleged omission to state therein any material fact necessary to make the statements made therein, in light of the circumstances under which the statements therein were made, not misleading (the matters in the foregoing clauses (i) and (ii) being, collectively, “Violations”). The Company shall reimburse the Investor promptly as such expenses are incurred and are due and payable, for properly documented reasonable legal fees or disbursements that are reasonably incurred by them or other reasonable expenses incurred by them in connection with investigating or defending any such Claim. Notwithstanding anything to the contrary contained herein, the indemnification agreement contained in this Section 6(a): (x) shall not apply to a Claim by an Indemnified Person arising out of or based upon a Violation which occurs in reliance upon and in conformity with information furnished in writing to the Company by such Indemnified Person expressly for use in connection with the preparation of the Registration Statement or any such amendment thereof or supplement thereto; (y) shall not be available to the extent such Claim is based on a failure of the Investor to deliver or to cause to be delivered the prospectus made available by the Company, if such prospectus was timely made available by the Company pursuant to Section 3(b); and (z) shall not apply to amounts paid in settlement of any Claim if such settlement is effected without the prior written consent of the Company, which consent shall not be unreasonably withheld. Such indemnity shall remain in full force and effect regardless of any investigation made by or on behalf of the Indemnified Person.


 
5 (b) In connection with a Registration Statement, the Investor agrees to indemnify, hold harmless, and defend, to the same extent and in the same manner as is set forth in Section 6(a), the Company, each of its directors, and each of its officers, employees, representatives, or agents and each Person, if any, who controls the Company within the meaning of the Securities Act or the Exchange Act (each an “Indemnified Party”), against any Claim or Indemnified Damages to which any of them may become subject, under the Securities Act, the Exchange Act, or otherwise, insofar as such Claim or Indemnified Damages arise out of or is based upon any Violation, in each case to the extent, and only to the extent, that such Violation occurs (i) in reliance upon and in conformity with written information furnished to the Company by the Investor expressly for use in connection with such Registration Statement or (ii) from the Investor’s violation of any prospectus delivery requirements under the Securities Act, the Exchange Act, any other law, including, without limitation, any state securities law, or any rule or regulation thereunder relating to the offer or sale of the Registrable Securities pursuant to a Registration Statement; and, subject to Section 6(d), such Investor will reimburse any legal or other expenses reasonably incurred by them in connection with investigating or defending any such Claim; provided, however, that the indemnity agreement contained in this Section 6(b) and the agreement with respect to contribution contained in Section 7 shall not apply to amounts paid in settlement of any Claim if such settlement is effected without the prior written consent of such Investor, which consent shall not be unreasonably withheld, conditioned, or delayed; provided, further, however, that, absent fraud or gross negligence, the Investor shall be liable under this Section 6(b) for only that amount of a Claim or Indemnified Damages as does not exceed the net proceeds to such Investor as a result of the sale of Registrable Securities pursuant to such Registration Statement. Such indemnity shall remain in full force and effect regardless of any investigation made by or on behalf of such Indemnified Party. Notwithstanding anything to the contrary contained herein, the indemnification agreement contained in Section 6(a) with respect to any prospectus shall not inure to the benefit of any Indemnified Person if the untrue statement or omission of material fact contained in the prospectus was corrected and such new prospectus was delivered to the Investor prior to such Investor’s use of the prospectus to which the Claim relates. (c) Promptly after receipt by an Indemnified Person or Indemnified Party under this Section 6 of notice of the commencement of any action or proceeding (including any governmental action or proceeding) involving a Claim, such Indemnified Person or Indemnified Party shall, if a Claim in respect thereof is to be made against any indemnifying party under this Section 6, deliver to the indemnifying party a written notice of the commencement thereof, and the indemnifying party shall have the right to participate in, and, to the extent the indemnifying party so desires, jointly with any other indemnifying party similarly noticed, to assume control of the defense thereof with counsel reasonably mutually satisfactory to the indemnifying party and the Indemnified Person or the Indemnified Party, as the case may be; provided, however, that an Indemnified Person or Indemnified Party shall have the right to retain its own counsel with the fees and expenses of not more than one (1) counsel for such Indemnified Person or Indemnified Party to be paid by the indemnifying party, if, in the reasonable opinion of counsel retained by the indemnifying party, the representation by such counsel of the Indemnified Person or Indemnified Party and the indemnifying party would be inappropriate due to actual or potential differing interests between such Indemnified Person or Indemnified Party and any other party represented by such counsel in such proceeding. The Indemnified Party or Indemnified Person shall cooperate fully with the indemnifying party in connection with any negotiation or defense of any such action or claim by the indemnifying party and shall furnish to the indemnifying party all information reasonably available to the Indemnified Party or Indemnified Person which relates to such action or claim. The indemnifying party shall keep the Indemnified Party or Indemnified Person fully apprised at all times as to the status of the defense or any settlement negotiations with respect thereto. No indemnifying party shall be liable for any settlement of any action, claim, or proceeding effected without its prior written consent; provided, however, that the indemnifying party shall not unreasonably withhold, delay, or condition its consent. No indemnifying party shall, without the prior written consent of the Indemnified Party or Indemnified Person, which consent shall not be unreasonably withheld, conditioned, or delayed, consent to entry of any judgment or enter into any settlement or other compromise which does not include as an unconditional term thereof the giving by the claimant or plaintiff to such Indemnified Party or Indemnified Person of a release from all liability in respect to such claim or litigation. Following indemnification as provided for hereunder, the indemnifying party shall be subrogated to all rights of the Indemnified Party or Indemnified Person with respect to all third parties, firms, or corporations relating to the matter for which indemnification has been made. The failure to deliver written notice to the indemnifying party within a reasonable time of the commencement of any such action shall not relieve such indemnifying party of any liability to the Indemnified Person or Indemnified Party under this Section 6, except to the extent that the indemnifying party is prejudiced in its ability to defend such action. (d) The indemnification required by this Section 6 shall be made by periodic payments of the amount thereof during the course of the investigation or defense, as and when bills are received or Indemnified Damages are incurred.


 
6 (e) The indemnity agreements contained herein shall be in addition to (i) any cause of action or similar right of the Indemnified Party or Indemnified Person against the indemnifying party or others, and (ii) any liabilities the indemnifying party may be subject to pursuant to applicable law. 7. CONTRIBUTION. To the extent any indemnification by an indemnifying party is prohibited or limited by law, the indemnifying party agrees to make the maximum contribution with respect to any amounts for which it would otherwise be liable under Section 6 to the fullest extent permitted by law; provided, however, that: (i) no Person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any Person who was not guilty of fraudulent misrepresentation; and (ii) contribution by any seller of Registrable Securities shall be limited in amount to the net amount of proceeds received by such seller from the sale of such Registrable Securities. 8. AMENDMENT OF REGISTRATION RIGHTS. Provisions of this Agreement may be amended and the observance thereof may be waived (either generally or in a particular instance and either retroactively or prospectively), with the written consent of the Company and the Investor. Any amendment or waiver effected in accordance with this Section 8 shall be binding upon each of the Investor and the Company. No consideration shall be offered or paid to any Person to amend or consent to a waiver or modification of any provision of any of this Agreement. 9. MISCELLANEOUS. (a) A Person is deemed to be a holder of Registrable Securities whenever such Person owns or is deemed to own of record such Registrable Securities. If the Company receives conflicting instructions, notices, or elections from two or more Persons with respect to the same Registrable Securities, the Company shall act upon the basis of instructions, notice, or election received from the registered owner of such Registrable Securities. (b) Any notices, consents, waivers, or other communications required or permitted to be given under the terms of this Agreement must be in writing and will be deemed to have been delivered pursuant to the notice provisions of the Purchase Agreement or to such other address and/or electronic mail address and/or to the attention of such other person as the recipient party has specified by written notice given to each other party five (5) days prior to the effectiveness of such change. Written confirmation of receipt (A) given by the recipient of such notice, consent, waiver, or other communication, (B) electronically generated by the sender’s email service provider containing the time, date, and recipient email, or (C) provided by a courier or overnight courier service shall be rebuttable evidence of personal service, receipt by facsimile, or receipt from a nationally recognized overnight delivery service in accordance with this Section 9(b). (c) Failure of any party to exercise any right or remedy under this Agreement or otherwise, or delay by a party in exercising such right or remedy, shall not operate as a waiver thereof. (d) The laws of the State of Delaware shall govern all issues concerning the relative rights of the Company and the Investor under this Agreement. All questions concerning the construction, validity, enforcement, and interpretation of this Agreement shall be governed by the internal laws of the State of Delaware, without giving effect to any choice of law or conflict of law provision or rule (whether of the State of Delaware or any other jurisdiction) that would cause the application of the laws of any jurisdiction other than the State of Delaware. Each party hereby irrevocably submits to the non-exclusive jurisdiction of the state and federal courts sitting in the City of Wilmington, New Castle County, State of Delaware, for the adjudication of any dispute hereunder or in connection herewith or with any transaction contemplated hereby or discussed herein, and hereby irrevocably waives, and agrees not to assert in any suit, action, or proceeding, any claim that it is not personally subject to the jurisdiction of any such court, that such suit, action, or proceeding is brought in an inconvenient forum or that the venue of such suit, action, or proceeding is improper. Each party hereby irrevocably waives personal service of process and consents to process being served in any such suit, action, or proceeding by mailing a copy thereof to such party at the address for such notices to it under this Agreement and agrees that such service shall constitute good and sufficient service of process and notice thereof. Nothing contained herein shall be deemed to limit in any way any right to serve process in any manner permitted by law. If any provision of this Agreement shall be invalid or unenforceable in any jurisdiction, such invalidity or unenforceability shall not affect the validity or enforceability of the remainder of this Agreement in that


 
7 jurisdiction or the validity or enforceability of any provision of this Agreement in any other jurisdiction. EACH PARTY HEREBY IRREVOCABLY WAIVES ANY RIGHT IT MAY HAVE, AND AGREES NOT TO REQUEST, A JURY TRIAL FOR THE ADJUDICATION OF ANY DISPUTE HEREUNDER OR IN CONNECTION HEREWITH OR ARISING OUT OF THIS AGREEMENT OR ANY TRANSACTION CONTEMPLATED HEREBY. (e) This Agreement shall inure to the benefit of and be binding upon the permitted successors and assigns of each of the parties hereto. (f) The headings in this Agreement are for convenience of reference only and shall not limit or otherwise affect the meaning hereof. (g) This Agreement may be executed in identical counterparts, both of which shall be considered one and the same agreement and shall become effective when counterparts have been signed by each party and delivered to the other party. Facsimile or other electronically scanned and delivered signatures (including any electronic signature covered by the U.S. federal ESIGN Act of 2000, Uniform Electronic Transactions Act, the Electronic Signatures and Records Act, or other applicable law), including by e-mail attachment, shall be deemed to have been duly and validly delivered and be valid and effective for all purposes of this Agreement. (h) Each party shall do and perform, or cause to be done and performed, all such further acts and things, and shall execute and deliver all such other agreements, certificates, instruments, and documents, as the other party may reasonably request in order to carry out the intent and accomplish the purposes of this Agreement and the consummation of the transactions contemplated hereby. (i) The language used in this Agreement will be deemed to be the language chosen by the parties to express their mutual intent and no rules of strict construction will be applied against any party. (j) This Agreement is intended for the benefit of the parties hereto and their respective permitted successors and assigns, and is not for the benefit of, nor may any provision hereof be enforced by, any other Person. [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


 
[Registration Rights Agreement] IN WITNESS WHEREOF, the Company and the Investor have caused this Registration Rights Agreement to be duly executed as of the date first above written. COMPANY: NAUTICUS ROBOTICS, INC. By: Name: John W. Gibson Jr. Title: President and Chief Executive Officer INVESTOR: MASTER INVESTMENT GROUP By: Name: Sheikh Abdulla Al Qassimi Title: CEO