The Interest of America in Sea Power, Present and Future

by A. T. Mahan

The inquiry being thus broad, Samana Bay and the island of St. Thomas are entitled to the pre-eminence here given to them, because they represent, efficiently and better than any other positions, the control of two principal passages into the Caribbean Sea from the Atlantic. The Mona Passage, on which Samana lies, between Santo Domingo and Puerto Rico, is particularly suited to sailing-vessels from the northward, because free from dangers to navigation. This, of course, in these days of steam, is a small matter militarily; in the latter sense the Mona Passage is valuable because it is an alternative to the Windward Passage, or to those to the eastward, in case of hostile predominance in one quarter or the other. St. Thomas is on the Anegada Passage, actually much used, and which better than any other represents the course from Europe to the Isthmus, just as the Windward Passage does that from the North American Atlantic ports. Neither of these places can boast of great natural strength nor of resources; St. Thomas, because it is a small island with the inherent weaknesses attending all such, which have been mentioned; Samana Bay, because, although the island on which it is is large and productive, it has not now, and gives no hope of having, that political stability and commercial prosperity which bring resources and power in their train. Both places would need also considerable development of defensive works to meet the requirements of a naval port. Despite these defects, their situations on the passages named entitle them to paramount consideration in a general study of the Caribbean Sea and the Gulf of Mexico. Potentially, though not actually, they lend control of the Mona and Anegada Passages, exactly as Kingston and Santiago do of the Windward.

For, granting that the Isthmus is in the Caribbean the predominant interest, commercial, and therefore concerning the whole world, but also military, and so far possessing peculiar concern for those nations whose territories lie on both oceans, which it now severs and will one day unite—of which nations the United States is the most prominent—granting this, and it follows that entrance to the Caribbean, and transit across the Caribbean to the Isthmus, are two prime essentials to the enjoyment of the advantages of the latter. Therefore, in case of war, control of these two things becomes a military object not second to the Isthmus itself, access to which depends upon them; and in their bearing upon these two things the various positions that are passed under consideration must be viewed—individually first, and afterwards collectively.

The first process of individual consideration the writer has asked the reader to take on faith; neither time nor space permits its elaboration here; but the reasons for choosing those that have been named have been given as briefly as possible. Let us now look at the map, and regard as a collective whole the picture there graphically presented.

Putting to one side, for the moment at least, the Isthmian points, as indicating the end rather than the precedent means, we see at the present time that the positions at the extremes of the field under examination are held by Powers of the first rank,—Martinique and Santa Lucia by France and Great Britain, Pensacola and the Mississippi by the United States.

Further, there are held by these same states of the first order two advanced positions, widely separated from the first bases of their power; namely, Key West, which is 460 miles from Pensacola, and Jamaica, which is 930 miles from Santa Lucia. From the Isthmus, Key West is distant 1200 miles; Jamaica, 500 miles.

Between and separating these two groups, of primary bases and advanced posts, extends the chain of positions from Yucatan to St. Thomas. As far as is possible to position, apart from mobile force, these represent control over the northern entrances—the most important entrances—into the Caribbean Sea. No one of this chain belongs to any of the Powers commonly reckoned as being of the first order of strength.

The entrances on the north of the sea, as far as, but not including, the Anegada Passage, are called the most important, because they are so few in number,—a circumstance which always increases value; because they are so much nearer to the Isthmus; and, very especially to the United States, because they are the ones by which, and by which alone,—except at the cost of a wide circuit,—she communicates with the Isthmus, and, generally, with all the region lying within the borders of the Caribbean.

In a very literal sense the Caribbean is a mediterranean sea; but the adjective must be qualified when comparison is made with the Mediterranean of the Old World or with the Gulf of Mexico. The last-named bodies of water communicate with the outer oceans by passages so contracted as to be easily watched from near-by positions, and for both there exist such positions of exceptional strength,—Gibraltar and some others in the former case, Havana and no other in the latter. The Caribbean, on the contrary, is enclosed on its eastern side by a chain of small islands, the passages between which, although practically not wider than the Strait of Gibraltar, are so numerous that entrance to the sea on that side may be said correctly to extend over a stretch of near 400 miles. The islands, it is true, are so many positions, some better, some worse, from which military effort to control entrance can be exerted; but their number prevents that concentration and that certainty of effect which are possible to adequate force resting upon Gibraltar or Havana.

On the northern side of the sea the case is quite different. From the western end of Cuba to the eastern end of Puerto Rico extends a barrier of land for 1200 miles—as against 400 on the east—broken only by two straits, each fifty miles wide, from side to side of which a steamer of but moderate power can pass in three or four hours. These natural conditions, governing the approach to the Isthmus, reproduce as nearly as possible the strategic effect of Ireland upon Great Britain. There a land barrier of 300 miles, midway between the Pentland Firth and the English Channel—centrally situated, that is, with reference to all the Atlantic approaches to Great Britain—gives to an adequate navy a unique power to flank and harass either the one or the other, or both. Existing political conditions and other circumstances unquestionably modify the importance of these two barriers, relatively to the countries affected by them. Open communication with the Atlantic is vital to Great Britain, which the Isthmus, up to the present time, is not to the United States. There are, however, varying degrees of importance below that which is vital. Taking into consideration that of the 1200-mile barrier to the Caribbean 600 miles is solid in Cuba, that after the 50-mile gap of the Windward Passage there succeeds 300 miles more of Haiti before the Mona Passage is reached, it is indisputable that a superior navy, resting on Santiago de Cuba or Jamaica, could very seriously incommode all access of the United States to the Caribbean mainland, and especially to the Isthmus.

In connection with this should be considered also the influence upon our mercantile and naval communication between the Atlantic and the Gulf coasts exercised by the peninsula of Florida, and by the narrowness of the channels separating the latter from the Bahama Banks and from Cuba. The effect of this long and not very broad strip of land upon our maritime interests can be realized best by imagining it wholly removed, or else turned into an island by a practicable channel crossing its neck. In the latter case the two entrances to the channel would have indeed to be assured; but our shipping would not be forced to pass through a long, narrow waterway, bordered throughout on one side by foreign and possibly hostile territories. In case of war with either Great Britain or Spain, this channel would be likely to be infested by hostile cruisers, close to their own base, the very best condition for a commerce-destroying war; and its protection by us under present circumstances will exact a much greater effort than with the supposed channel, or than if the Florida Peninsula did not exist. The effect of the peninsula is to thrust our route from the Atlantic to the Gulf 300 miles to the southward, and to make imperative a base for control of the strait; while the case is made worse by an almost total lack of useful harbors. On the Atlantic, the most exposed side, there is none; and on the Gulf none nearer to Key West than 175 miles,[^[2] ] where we find Tampa Bay. There is, indeed, nothing that can be said about the interests of the United States in an Isthmian canal that does not apply now with equal force to the Strait of Florida. The one links the Atlantic to the Gulf, as the other would the Atlantic to the Pacific. It may be added here that the phenomenon of the long, narrow peninsula of Florida, with its strait, is reproduced successively in Cuba, Haiti, and Puerto Rico, with the passages dividing them. The whole together forms one long barrier, the strategic significance of which cannot be overlooked in its effect upon the Caribbean; while the Gulf of Mexico is assigned to absolute seclusion by it, if the passages are in hostile control.