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Bill Thayer

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This webpage reproduces an article in
Journal of the United States Artillery
Vol. 44 (1915), pp159‑163

The text is in the public domain.

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 p159  From Harbor Defense
to Coast Defense

By Colonel Indicates a West Point graduate and gives his Class.Charles A. Bennett,
Coast Artillery Corps

The lessons of the European war attract public attention to ways and means of defense against possible attack and invasion from the sea. The large armies abroad, now trained in modern warfare, combined with the great development of modern transport, constitute a standing menace in view of our small army of limited experience in warfare and the foreign policy which our people demand. Whether or not actual danger threatens, the menace should give way to a feeling of security whereby diplomacy would not be hampered.

The fact of such menace implies an admission that the coast defense may fail. The so‑called Coast Defense — Harbor Defense in reality — can defend only within range of the guns and can not prevent hostile landing elsewhere even for operations against itself. It is immobile. Whether or not a hostile force once landed could maintain itself against our land forces, the navy alone could prevent the actual landing.

The navy has a wide field of operations including not only the Atlantic and Pacific seaboards but the Panama canal and outlying possessions. Naval strategy demands that fleets have freedom of action and that they be not tied to the coast.

Advantage of initiative to the offense, now accentuated by wireless communication, is such that in any serious attempt at attack or invasion the hostile navy should be superior upon arriving at the objective. While such attempt would probably demand defense by our fleets yet some time might be necessary for their mobilization in sufficient force to be effective. This time would be an asset to the enemy. A local success might result in much destruction or in a levy of large amount. The great range of modern guns on ships may even permit of bombardment of coast cities from positions beyond effective range of harbor defenses. Even undefended cities may be subject to bombardment. While such would be prohibited by international law, yet an enemy could resort to "reprisals"  p160 at his pleasure. Admitting that the ultimate success of the invading force would depend upon control of the sea, it is not pleasant to contemplate operations on our soil or possible danger to coast cities.

That such condition exists invites no criticism. It is common to all countries but of less importance to those with large armies and small extent of coast. The defect is the immobility of the harbor defense and the necessity for use of the navy at widely separated points; a defect heretofore without remedy.

Attempt at remedy, involving the tacit admission that landings are practicable, has been made through plans of defense by mobile troops, assuming land operations near the coast. However effective coast defense may ultimately become, such plans would continue to be advisable.

A real remedy has but recently appeared through the development of two new weapons of warfare — aircraft and the submarine. These are mobile, effective, and admirably adapted to coast defense. They could at once expand harbor defense into that mobile coast defense which is demanded.

With attempt at attack or invasion, they would tend to decide the issue at the shore line where the coast defense should have superiority rather than on land where the enemy might easily be superior. They could offer effective reply to long range bombardment of coast cities. The enemy would be attacked in his ships before he could utilize his resources for land warfare. The weapons would be chosen by us, not by him.

These weapons have already exercised great influence in the existing war. They are rapidly developing greater efficiency and their ultimate power can only be surmised.

It may be anticipated that aircraft, as they increase in size and in ability to carry weight, will develop into an efficient means of attack upon ships. Since aircraft alone can observe mines and submarines below the surface, it can be expected that they will become the enemy of each, either by direct attack when able safely to fly low or through auxiliary small fast boats guided by signal. Possibly, for harbors and smooth waters, the fast hydro-boat might be developed for such purpose, mounting light guns for attack of submarines as they rise. If so, coast defense should profit since such auxiliaries of an enemy would have to be transported a long distance.

 p161  Control of the air will become important. Assuming that aircraft will become effective in attack of submarines, control of the air would prevent attack of our submarines and expose to attack those of the enemy. The resulting free action of our submarines against bombarding ships or against the large amount of shipping necessary to an invading force of sufficient size to be a menace, should effectually prevent success of the hostile attempt.

If this be correct, then control of the air at the seacoast will become as important against attack and invasion as is the control of the sea as now understood, and the United States should have and retain control of the air of its own seaboard.

Destructive as is the torpedo of the submarine, the submarine has a great moral effect apparent from its actual efficiency. The ever present fear of those on ships that a submarine may appear at any time is a great moral factor.

When aircraft become effective in overhead attack upon ships, this same moral effect will attach to that weapon. To obtain full value of this, aircraft and submarines should be along the entire coast. These weapons would favor coast defense. While an enemy may easily bring across the sea his fleets with transports, fuel and supply ships, transport of aircraft and submarines should present such difficulties relative to the defense operating at its base as to ensure superiority to the latter in such weapons and their auxiliaries.

For an effective coast defense, a large number of submarines and a much larger number of aircraft would be needed. Will they be provided for this purpose?

For attack of countries across the sea, involving long ocean travel, they would be of little use, In so far as this country is concerned, they would be elsy defensive weapons. As such, their use should appeal to the people including the so‑called "peace party." The latter as individuals secure their homes and valuables against intruders. Solicitatiousº as they are for the general welfare, it could be expected they would give full support to purely defensive measures designed for protection of thousands of homes against possible predatory nations. If not, it would be interesting to know why they distrusted human nature in the individual and trusted it in the large masses.

Should these weapons be provided for coast defense,  p162 the organization to attain a maximum efficiency would be important. In addition to their use with fleets, they would be needed for harbor defense and for such patrol and observation of the coast as to impart a moral deterrent effect and to ensure adequate protection to commerce and freedom from bombardment by raiding ships. At a few important points, preferably navy yards, should be reserves in readiness.

These weapons are needed in harbor defense not only to combat activities of similar weapons of the enemy which would now be present but to prevent landing operations and to assist generally in the defense. An invading force of such strength as to be a real danger would probably need a harbor as a base. To obtain such, it would resort to combined land and naval attack.

His aircraft would be useful to him for following purposes:

Observation and correction of his fire.

Reconnaissance of all elements of the defense.

Overhead attack of batteries and other elements.

Location of mines and submarines.

His submarines could:

Operate against mines.

Operate against shipping, in harbor or elsewhere.

A rational organization to meet the requirements would be as follows:

a. Division of the coast lines into zones of defense, with bases in designated harbors.

b. Combination of zones into districts.

c. Assignment to zones and districts of elements of defense.

d. Observation of each zone by aircraft.

e. Patrol of each zone by submarine.

f. System of wireless communication.

g. Prompt concentration at any threatened point of all elements of defense, including aircraft, submarines, coast guard troops, available naval forces; resources of adjacent zones and districts to be utilized as needed.

Since any such operation would imply local control of the sea by the enemy, submarines could strew mines over the threatened water area — a suitable type being developed.

Aircraft and submarines would work well together, the former to observe and indicate targets to the latter at the same time offering protection from attack of the latter by  p163 hostile aircraft. Operating thus, they would be under the same organization. At present, submarines are exclusively naval.

Should these weapons be supplied to harbor defenses whereby the commanders of such defenses became commanders of zones, then the independent action of zone commanders and naval commanders would invite confusion as to conduct of the defense and in identity of individual aircraft and submarines, whenever acting together.

Probably a more satisfactory organization would be to have the mobile defense entirely naval, in which case the commander of the harbor defense and the commander of the zone would co‑operate. In any event, some officer other than the commander of the harbor defense would be in immediate command of the mobile defense. These new weapons required alike by the navy and the harbor defenses have linked these services together in the common field of coast defense. Both economy and the attainment of a maximum efficiency would require an organization necessary to concert of action. It is even possible that future development of coast defense may show the desirability of merging the Coast Artillery Corps into the Navy as a special branch whereby coast defense in its entirety would be under one Department head.

During peace, a large proportion of submarines and aircraft could be kept out of commission. Personnel for such should be obtained by a system of reserves whereby officers and men, trained during a period of service with the colors, would be immediately available at mobilization. The question of personnel would probably be one of the most difficult of solution. The time has almost arrived to solve the question and to shape the future policy as to defense of the coast. When proper provision for such defense has been made, mobilization will probably be unnecessary.

While it may not be possible at present to bring naval strength to a parity with that of other powers now in the lead — perhaps not necessary — yet it is now possible to keep abreast of any power in submarines and aircraft which are so well adapted to our needs in view of the large extent of seaboard and the great wealth that lies thereon.

Important as are guns, mortars and harbor mines, yet, with development of submarines and aircraft, the older weapons may be expected to gradually yield in first importance.

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Page updated: 1 Jun 14