Mr. Justice Stone
delivered the opinion of the Court.
This case is here on appeal, § 237 Jud. Code, as amended by the Act of January 31, 1928, from a judgment of the Court of Appeals of Maryland, 159 Md. 334; 151 Atl. 29, which upheld an order of appellee, the State Tax Commission, assessing 2110 acres of appellant’s submerged lands, for 1929 taxation, at $2,349,300.
Appellant is a licensee of the Federal Power Commission, created under the Act of June 10, 1920, c. 285, 41 Stat. 1063. Acting under the license, it has constructed a dam across the Susquehanna River which, for present purposes, we assume to be navigable, and has established an adjacent power plant at a point within the State. As a part of the power project, it acquired by purchase from private owners, and by grant from the State, large areas of land, including the bed of the river and adjoining upland. On completion of the dam, the waters of the Susquehanna were backed up, forming a pool about fourteen miles in length, and submerging a large area formerly upland, including a town site, and land previously occupied and used as a canal. The lands assessed by appellee lie under the pool created by appellant’s dam, and are used, and derive their chief value, as a part of the power project.
In the present suit, brought to review the order of the Commission fixing the assessment, appellant assailed its action, taken under Laws of Maryland; 1914, c. 841; Bagby, Ann. Code (1924), Art. 81, § 249 (2), directing assessment of property for taxation, as in conflict with the Federal Constitution. Appellant urges, as principal grounds for reversal, first, that in constructing and operating its power plant under the federal license, it, and its lands and property used in the power project, are agencies