Exhibit 99.1

To All Employees

Dear Colleagues, 

Since the recent announcement about our proposed merger with Ensco, the senior leadership team and I have been focused on answering as many of your questions as we can with the information available. I understand many of you will feel apprehensive about the merger, but I want you to know I remain committed to keeping you informed as we learn more and make important decisions about our plans for the integration of the two companies.

This past week, we met with many important stakeholders (especially shareholders and customers), and I am extremely pleased with the mostly positive reaction to the proposed merger. Positive responses have also been received from our customers, and many are excited about the potential for technology development by the combined company. The investment community recognizes that industry consolidation is needed and that this merger will create a stronger, more diversified driller. 

This week I met Carl Trowell and Carey Lowe, Ensco’s CEO & COO, respectively, in London to discuss integration pre-planning. You should expect to hear news about the integration planning team and integration “kick-off” in the next two weeks. We plan to continue providing updates on the proposed merger and integration plans of the two companies as information becomes available. Updates will be sent via email and posted on the new Rowan and Ensco Merger pages on DrillNet and Rig Home.

I am excited about this next step for Rowan, and the significant opportunities the merger will present for the company, although we are still needing to address various closing conditions. Please continue to be patient as we continuously work through the plan, and thank you for remaining focused on safe, efficient, and reliable operations. 

Regards,

Tom Burke

Forward-Looking Statements

Statements included in this document regarding the proposed transaction, benefits, expected synergies and other expense savings and operational and administrative efficiencies, opportunities, timing, expense and effects of the transaction, financial performance, accretion to discounted cash flows, revenue growth, future dividend levels, credit ratings or other attributes of Ensco plc (“Ensco”) following the completion of the transaction and other statements that are not historical facts, are forward-looking statements (including within the meaning of Section 21E of the Securities Exchange Act of 1934, as amended, and Section 27A of the Securities Act of 1933, as amended (the “Securities Act”)). Forward-looking statements include words or phrases such as “anticipate,’ “believe,” “contemplate,” “estimate,” “expect,” “intend,” “plan,” “project,” “could,” “may,” “might,” “should,” “will” and words and phrases of similar import. These statements involve risks and uncertainties including, but not limited to, actions by regulatory authorities, rating agencies or other third parties, actions by the respective companies’ security holders, costs and difficulties related to integration of Rowan Companies plc (“Rowan”), delays, costs and difficulties related to the transaction, market conditions, and Ensco’s financial results and performance following the completion of the transaction, satisfaction of closing conditions, ability to repay debt and timing thereof, availability and terms of any financing and other factors detailed in the risk factors section and elsewhere in Ensco’s and Rowan’s Annual Report on Form 10-K for the year ended December 31, 2017 and their respective other filings with the Securities and Exchange Commission (the “SEC”), which are available on the SEC’s website at www.sec.gov. Should one or more of these risks or uncertainties materialize (or the other consequences of such a development worsen), or should underlying assumptions prove incorrect, actual outcomes may vary materially from those forecasted or expected. All information in this document is as of today. Except as required by law, both Ensco and Rowan disclaim any intention or obligation to update publicly or revise such statements, whether as a result of new information, future events or otherwise.

Important Additional Information Regarding the Transaction Will Be Filed With the SEC

In connection with the proposed transaction, Ensco and Rowan will file a joint proxy statement on Schedule 14A with the SEC. To the extent Ensco effects the proposed transaction as a court-sanctioned scheme of arrangement between Rowan and Rowan’s shareholders under the UK Companies Act of 2006, as amended, the issuance of Ensco’s ordinary shares in the proposed transaction would not be expected to require registration under the Securities Act, pursuant to an exemption provided by Section 3(a)(10) under the Securities Act. In the event that Ensco determines, with Rowan’s consent, to structure the transaction as an offer or otherwise in a manner that is not exempt from the registration requirements of the Securities Act, Ensco will file a registration statement with the SEC containing a prospectus with respect to Ensco’s ordinary shares that would be issued in the proposed transaction. INVESTORS AND SECURITY HOLDERS OF ROWAN ARE ADVISED TO CAREFULLY READ THE JOINT PROXY STATEMENT AND ANY REGISTRATION STATEMENT/PROSPECTUS (INCLUDING ALL AMENDMENTS AND SUPPLEMENTS THERETO) WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE TRANSACTION, THE PARTIES TO THE TRANSACTION AND THE RISKS ASSOCIATED WITH THE TRANSACTION. A definitive joint proxy statement and any registration statement/prospectus, as applicable, will be sent to security holders of Rowan in connection with Rowan’s shareholder meetings. Investors and security holders may obtain a free copy of the joint proxy statement (when available), any registration statement/prospectus, and other relevant documents filed by Rowan with the SEC from the SEC's website at www.sec.gov. Security holders and other interested parties will also be able to obtain, without charge, a copy of the joint proxy statement, any registration statement/prospectus, and other relevant documents (when available) by directing a request by mail or telephone to Investor Relations, Rowan Companies plc, 2800 Post Oak Boulevard, Suite 5450, Houston, Texas 77056, telephone 713-621-7800. Copies of the documents filed by Rowan with the SEC will be available free of charge on Rowan’s website at www.rowan.com/investor-relations.

Participants in the Solicitation

Rowan and its directors, executive officers and certain other members of management may be deemed to be participants in the solicitation of proxies from its security holders with respect to the transaction. Information about these persons is set forth in Rowan’s proxy statement relating to its 2018 General Meeting of Shareholders, as filed with the SEC on April 3, 2018 and subsequent statements of changes in beneficial ownership on file with the SEC. Security holders and investors may obtain additional information regarding the interests of such persons, which may be different than those of Rowan’s' security holders generally, by reading the joint proxy statement, any registration statement and other relevant documents regarding the transaction, which will be filed with the SEC.

No Offer or Solicitation

This document is not intended to and does not constitute an offer to sell or the solicitation of an offer to subscribe for or buy or an invitation to purchase or subscribe for any securities or the solicitation of any vote in any jurisdiction pursuant to the proposed transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in contravention of applicable law. Subject to certain exceptions to be approved by the relevant regulators or certain facts to be ascertained, the public offer will not be made directly or indirectly, in or into any jurisdiction where to do so would constitute a violation of the laws of such jurisdiction, or by use of the mails or by any means or instrumentality (including without limitation, facsimile transmission, telephone and the internet) of interstate or foreign commerce, or any facility of a national securities exchange, of any such jurisdiction.

Service of Process

Rowan is incorporated under the laws of England and Wales. In addition, some officers and directors reside outside the United States, and some or all of its assets are or may be located in jurisdictions outside the United States. Therefore, investors may have difficulty effecting service of process within the United States upon those persons or recovering against Rowan or its officers or directors on judgments of United States courts, including judgments based upon the civil liability provisions of the United States federal securities laws. It may not be possible to sue Rowan or its officers or directors in a non-U.S. court for violations of the U.S. securities laws.