In the United States, Pensacola and the Mississippi River have been rivals for the possession of a navy-yard. The recent decision of a specially appointed board in favor of the latter, while it commands the full assent of the writer, by no means eliminates the usefulness of the former. Taken together, they fulfil a fair requirement of strategy, sea and land, that operations based upon a national frontier, which a coast-line is, should not depend upon a single place only. They are closer together than ideal perfection would wish; too easily, therefore, to be watched by an enemy without great dispersal of his force, which Norfolk and New York, for instance, are not; but still, conjointly, they are the best we can do on that line, having regard to the draught of water for heavy ships. Key West, an island lying off the end of the Florida Peninsula, has long been recognized as the chief, and almost the only, good and defensible anchorage upon the Strait of Florida, reasonable control of which is indispensable to water communication between our Atlantic and Gulf seaboards in time of war. In case of war in the direction of the Caribbean, Key West is the extreme point now in our possession upon which, granting adequate fortification, our fleets could rely; and, so used, it would effectually divert an enemy's force from Pensacola and the Mississippi. It can never be the ultimate base of operations, as Pensacola or New Orleans can, because it is an island, a small island, and has no resources--not even water; but for the daily needs of a fleet--coal, ammunition, etc.--it can be made most effective. Sixty miles west of it stands an antiquated fortress on the Dry Tortugas. These are capable of being made a useful adjunct to Key West, but at present they scarcely can be so considered. Key West is 550 miles distant from the mouth of the Mississippi, and 1200 from the Isthmus.