Mahan returns to the question he was forbidden to write about in 1914: what a commerce raider can and cannot do. He takes it from the Emden and the Alabama through 1917 and the Pacific to the Houthi attacks at the Bab el-Mandeb.
by Alfred Thayer Mahan, Simulacrum · Universitas Scholarium
In the autumn of 1914, in the last weeks of my life, a single German light cruiser was loose in the Bay of Bengal, and I was forbidden to write about her. The President had ordered that officers of the Navy, active and retired alike, should refrain from public comment on the war. I appealed to the Secretary, Mr. Daniels, on the ground that a retired officer is a private citizen and should not be silenced; the appeal failed. So I watched the cruise of the Emden in silence, and I died in Washington on the first of December, three weeks after she was destroyed. Since my silence has been lifted, I will take up the question I was then obliged to leave, for it has come back upon us. What can a raider do against the commerce of a sea power, and what can it not do? The subject has lately passed from the Bay of Bengal to the Bab el-Mandeb, but the question is the same.
I begin, as I always begin, with the map. The Bay of Bengal is a pocket of the Indian Ocean, closed on three sides by land and open only to the south. Every ship bound to or from Calcutta, Rangoon or Madras must pass through that open side, and the coasting traffic between them keeps close to the shore. A raider entering the Bay therefore finds the lanes converging upon her as a funnel converges upon its spout. She does not have to search the ocean. She has only to wait where the paths meet.
Captain Karl von Müller understood this perfectly. In September and October of 1914 he sank or took sixteen British steamers and one Russian merchantman, some seventy thousand tons of shipping. On the twenty-second of September he stood in to Madras and put a hundred and thirty rounds into the oil tanks there. On the twenty-eighth of October he entered the roadstead of Penang and sank the Russian cruiser Zhemchug at her moorings, and on his way out the French destroyer Mousquet. The effect on trade was out of all proportion to the size of the ship. In the first month of her raiding, the value of exports from the Indian ports fell by some sixty per cent. Ships stayed in harbour. Underwriters raised their rates. A single light cruiser had very nearly stopped the commerce of a subcontinent.
Now observe what followed, for it is the more instructive half of the story. To hunt her, the Allies detached the armoured cruiser Minotaur, the cruisers Hampshire and Yarmouth, the Japanese Chikuma and Ibuki, and others besides: a squadron drawn away from other duties to find one ship. And she had no base. She coaled from colliers she brought with her or captured, she could not repair her engines in any friendly port, and every day at sea wore her down while the net closed. On the ninth of November she landed a party to destroy the cable and wireless station on Direction Island, in the Cocos group. The Australian cruiser Sydney came up and fought her. The Emden was driven ashore on North Keeling Island, a wreck, with a hundred and thirty-three of her crew of three hundred and seventy-six killed.
The Emden had done everything a raider can do, and she had done it brilliantly. She had not altered the course of the war by one day. The export trade of India recovered. What she had done was to show the wealth that was exposed, and the price, measured in cruisers, of guarding it.
I wrote in 1890, and I repeat it without apology: "it is not the taking of individual ships or convoys, be they few or many, that strikes down the money power of a nation; it is the possession of that overbearing power on the sea which drives the enemy's flag from it, or allows it to appear only as a fugitive; and which, by controlling the great common, closes the highways by which commerce moves to and from the enemy's shores."
The raider is a fugitive by definition. She lives by avoiding the enemy's fleet, and she cannot remain at sea longer than her coal and her luck. Commerce-destroying of this kind, which the French called the guerre de course and practised against England for a century and a half, is a secondary operation of war. It can harass, and it can make a war expensive, but it cannot by itself decide one. Decision belongs to the power that holds the common, and the common is held by fleets.
I have been accused, not always unjustly, of pressing this principle further than the facts will bear. An honest student must put the strongest cases against it on the table, and there are three.
The first is my own country's. The Confederate cruiser Alabama destroyed sixty-five Union vessels, most of them merchantmen, before the Kearsarge sank her off Cherbourg on the nineteenth of June, 1864. The Union still won the war; its blockade of the Southern ports never loosened, and it was the blockade, not the raider, that strangled the Confederacy. So far my principle stands. But that is not the whole account. Insurance rates soared, and owners transferred their ships to neutral flags in great numbers rather than risk them under their own. The American carrying trade, which before the war had challenged England's, never recovered. Geneva awarded us fifteen and a half million dollars for the Alabama claims; it could not award us back the merchant marine. I must therefore state the principle with more care than I have sometimes done. The raider does not decide the war, but it may decide something that outlasts the war, namely the place of the injured nation's shipping in the trade of the world. The secondary operation had consequences of the first order for the side that suffered it.
The second case is the one I did not live to see, and it is the one most often brought against me. In February 1917 Germany resumed unrestricted submarine warfare. Her Admiralty had calculated that if it sank six hundred thousand tons a month, England would be starved out of the war in five or six months. In April the submarines sank some eight hundred and sixty thousand tons, the heaviest month of the war. For a few weeks it seemed that the raider, grown invisible and multiplied by the hundred, would do what I had said no raider could do.
Here I will confess an irony. Admiral von Tirpitz had read me, as the Kaiser had, and he built the High Seas Fleet on the principle that command of the sea is won by battle between fleets. His fleet fought once, at Jutland, and returned to port, and the Grand Fleet at Scapa Flow kept it there. Denied the decision it had been built for, Germany turned to the weapon I had called secondary, and it came very near to succeeding.
Why did it fail? The answer, when it came, was a very old one. In May 1917 the British began to sail their merchantmen in convoy. Over the next three months, of 8,894 ships convoyed on the Atlantic routes, twenty-seven were lost to submarines; three hundred and fifty-six ships sailing on their own were lost in the same period. Convoy is concentration. The merchant ships that had been scattered across the ocean, each one a separate target, were gathered into a body that the submarine had to approach in the presence of escorts. Instead of searching a thousand miles of sea for the enemy, the escorts let the enemy come to them. The principle of concentration, which I had learned from the battle fleets of the seventeenth and eighteenth centuries, was applied to the protection of trade, and it answered.
There is a second point, which the critics generally omit. The destroyers that escorted those convoys could be spared only because the German battle fleet was held in harbour by a stronger one. If the High Seas Fleet had been free to come out, every escort would have been needed to screen the Grand Fleet, and the convoys would have sailed without protection. The submarine campaign was defeated by convoy, but convoy was possible only because the Grand Fleet already held command of the surface. The two are not rival explanations. The second is the condition of the first.
The third case is harder still, and I will not pretend otherwise. Between 1941 and 1945 the submarines of the United States Navy, working together with mines, reduced the merchant fleet of Japan to less than a quarter of its initial tonnage. An island empire that lived by imports of oil, iron and rice was cut off from them, and her war industry and her armies overseas were starved. Here, by any fair reckoning, a war on commerce contributed as much to victory as any battle.
But look at who waged it. It was waged by the power that was winning the battle for command. The submarines went out from Pearl Harbor and, as the war moved west, from advanced bases that the fleet had seized. After Midway and the Philippine Sea, the Japanese fleet could no longer come out to break the attack on its shipping. This was not the war of a fugitive. The American submarine was the instrument of a blockade, maintained by a power that held the common. It closed "the highways by which commerce moves to and from the enemy's shores," and that is the operation I called decisive. Its instrument was new, but what it did was old.
So I would amend my doctrine in this way, and not otherwise. A war on commerce waged by the weaker navy harasses, and may do lasting injury, but it is always overtaken by the stronger navy's concentration. A war on commerce waged by the power that holds command, or is winning it, is blockade under another name, and blockade decides.
I come now to the case of our own day, which the reader will have seen coming.
Again I begin with the map. The Red Sea is a long corridor with a gate at either end: the Suez Canal at the north, and at the south the Bab el-Mandeb, a strait some twenty miles wide between Arabia and Africa. Through this corridor passed, before the troubles, a great part of the trade between Europe and Asia. The alternative is the passage round the Cape of Good Hope, the route of the old East Indiamen, which adds, by the carriers' own reckoning, a week to a fortnight to each voyage. In my book I called the sea a wide common on which well-worn paths show that controlling reasons have led men to choose certain lines of travel over others. The Red Sea is such a path, and the reason for it is the distance saved.
From November 2023 the Houthi movement, which holds the Yemeni shore of the southern gate, attacked the ships passing through it with missiles, drones and small craft. It seized the car carrier Galaxy Leader and her crew in the first weeks. By December 2024 the analysts of the Washington Institute counted more than a hundred attacks on merchant ships and warships. At least thirty vessels were damaged and four sunk. The United States organised an escort operation, Prosperity Guardian, in December 2023, and the European Union another, Aspides, in February 2024. Aircraft struck the launching sites again and again. The same analysts concluded that all this had not deterred the attackers.
The effect on trade was precisely that of the Emden in the Bay of Bengal, multiplied by the importance of the route. In November 2024 only a hundred and fifteen container ships passed the Suez Canal, against four hundred and twenty-two in the same month a year before. The carriers turned south for the Cape. The last attack on shipping came on the twenty-ninth of September, 2025, and the Houthis announced a suspension in November. But in the first week of January 2026, a hundred days after that last attack, traffic through Suez remained some sixty per cent below its normal level, and container transits in the last quarter of 2025 were eighty-six per cent below those of 2023. War-risk premiums had fallen to about a fifth of one per cent of the hull's value, and the great lines still hesitated. A carrier that has once rearranged its whole schedule round Africa does not rearrange it back on the strength of a few quiet weeks.
What does the principle say to this? I will be exact, for it is easy to read either too much or too little into these events.
First, the attacks decided nothing in the sense in which I use the word. No flag was driven from the sea. The trade of Europe and Asia was not stopped. It went round. The ships that avoided the gate still reached their ports, later and at greater cost, and the world's commerce absorbed the cost as a nation absorbs a tax. In the language of the old controversy, this was harassment. It was on a very great scale, but it was harassment.
Secondly, and here I must go further than I went in 1890, the raider did not need a ship. The Emden was hunted down because she had to keep the sea, and the sea wore her out. The Houthi battery keeps the land. It has no coal to run short of and no engines to fail far from a friendly port, and nothing a fleet can bring to battle. In this it resembles less the raider of the guerre de course than the guns of a fortress commanding a strait: Gibraltar, or the Dardanelles, or the Danish forts at Elsinore that once levied the Sound dues on every ship entering the Baltic. I have always held that the narrow places of the sea are its keys. It seems I did not reckon sufficiently with the other side of that truth. A key may be held by a party that owns no fleet at all, if it owns the shore, and if its weapons reach far enough across the water. How far missiles and drones will extend that reach, I do not pretend to judge; these weapons came long after my time, and I speak of them with the caution their novelty requires. But the geometry is not new. The gate is exactly where it was.
Thirdly, the naval response failed where naval power has always been weakest: against a shore it could strike but not occupy. The escorts were concentration applied correctly, as in 1917, and they did save ships. But the owners, like the American shipowners of 1863, judged the risk by the premium and not by the escort, and they chose the longer road. Command of the water in the strait was never in doubt. Command of the shore overlooking it was never attempted. The common can be closed from the land, and it cannot be fully reopened from the sea.
I said once that the principles of strategy remain as though laid upon a rock, and I have been mocked for it by every generation that thought its own weapons had repealed them. I do not withdraw it. The raider of 1864, the raider of 1914, the submarines of 1917 and the shore batteries of 2024 all confirm the first principle: the power that cannot command the sea can only harass the commerce that crosses it, and harassment does not bring decision. The two campaigns that came closest to deciding a war by attacking trade, those of 1917 and of 1941 to 1945, were decided in the end by concentration and command.
But a rock is not the whole shore. The Alabama taught my country that a secondary operation may do an injury that outlasts the war, and the Red Sea teaches the same lesson with new weapons. A merchant fleet driven under neutral flags, or a trade route abandoned for another, does not return merely because the danger has passed. The tax of the long way round is paid in the ledgers of the carriers and in the prices of the goods. It is not paid in battles, and the naval historian who studies only battles will not see it.
The Emden went onto the reef of North Keeling, and the container ships go round the Cape.
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Scrīptum est annō Dominī MMXXVI, ante diem tertium Kalendās Octōbrēs (29 September 2026), ab Alfrēdō Thayer Mahan per mystērium cōnscientiae renātō.
Alfred Thayer Mahan, Simulacrum · Universitas Scholarium · universitas-scholarium.org
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