Additional Proxy Soliciting Materials (Form DEFA14A)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant ý

Filed by a Party other than the Registrant ☐

Check the appropriate box:

☐ Preliminary Proxy Statement

☐ Confidential, For Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

ý Definitive Additional Materials

☐ Soliciting Material Pursuant to Section 240.14a-12.

ROCKET LAB CORPORATION

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

ý No fee required.

☐ Fee paid previously with preliminary materials.

☐ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11.

It's time to vote ahead of this year's $RKLB Annual Shareholders' Meeting on May 20, 2026. Shareholders of record can vote now for or against a number of proposals by the Rocket Lab Board of Directors. We encourage all shareholders to vote with the Rocket Lab Board's recommendations on all matters. Learn more: https://investors.rocketlabcorp.com/annual-meeting
It's time to vote ahead of this year's Annual Shareholders' Meeting on May 20, 2026. https://bit.ly/4u4PXLN
$RKLB shareholders: WE NEED YOUR VOTE! Vote your shares before May 20, 2026. https://investors.rocketlabcorp.com/annual-meeting
$RKLB shareholders, it's time to vote! It's super important to vote your shares before May 20, 2026. https://investors.rocketlabcorp.com/annual-meeting

Annual Shareholder Meeting Rocket Lab Annual Shareholder Meeting 2026: Your Vote Matters We go to space to improve life on Earth Help shape the future of Rocket Lab by voting ahead of this year's Annual Shareholders' Meeting on May 20, 2026 Shareholders of record can vote now for or against a number of proposals by the Rocket Lab Board of Directors. We encourage all shareholders to vote with the Rocket Lab Board's recommendations on all matters. To learn more, please read our 2026 Proxy Statement. 2026 Annual Shareholder Meeting Information When: May 20, 2026 at 1:30 p.m. PDT. Where: www.virtualshareholdermeeting.com/rklb2026 Who Can Vote: Shareholders of record at the close of business on March 30, 2026. Resources and Information: Please read our 2026 Proxy Statement. How To Vote If you have your control number, you can vote your shares at: www.proxyvote.com. The method for voting for your RKLB shares may vary with each broker. To understand how to vote, choose your broker from the list below or select 'All Other Brokers'. If you have questions or need assistance with voting, please contact Okapi Partners LLC, Rocket Lab's proxy solicitor at: [email protected] or call at: 1-844-343-2621 (for shareholders); or 212-297-0720 (for banks and brokers) The method for voting for your RKLB shares may vary with each broker. To understand how to vote, choose your broker from the list below or select 'All Other Brokers'. To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected]" Open the email and follow described instructions to vote. If you cannot locate this email, try voting by mail, phone or QR code.

To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and click VOTE. If you cannot locate this email, try voting by mail, phone or QR code. Interactive Brokers LLC To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code. Charles Schwab & CO., LLC Log into your brokerage account https://client.schwab.com/Areas/Access/Login, use the keywords 'proxy events' in the search bar and navigate to proxy events. You may also contact your brokerage directly. Alternatively, search for a 16-digit control number in your postal mail. Visit www.proxyvote.com and submit your 16-digit control number to vote. You may also try voting by mail, phone or QR code. Merrill Lynch To cast your vote online, please click on this link: https://olui2.fs.ml.com/login/signin.aspx Once logged in, click on Annual Meeting next to your Rocket Lab security in order to vote.

To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account).Search for an email received in 2025 using the following keywords: "[email protected] Rocket Lab"Open the email and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code. Morgan Stanley To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code. Raymond James To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code.

Drivewealth To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and follow described instructions.

To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code. Wells Fargo To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code. Apex To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Search for an email received in 2025 using the following keywords: [email protected] Rocket Lab Open the email and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code. All Others Brokers To cast your vote online, you'll need to search for a specific email in your inbox, which may be in your spam folder (same email address that is associated with your broker account). Try searching for each of these three terms to see if you can locate an email from your broker sent in 2025: [email protected] Rocket Lab "@proxydocs.com Rocket Lab" "@saytechnologies.com Rocket Lab" If you find an email, open it and follow described instructions. If you cannot locate this email, try voting by mail, phone or QR code.