Πολυκράτης γὰρ ἐστὶ πρῶτος τῶν ἡμεῖς ἵδμεν Ἑλλήνων ὃς θαλασσοκρατέειν ἐπενοήθη.For Polycrates was the first of the Greeks we know who intended to rule the sea.
Herodotus, The Persian Wars, III:122, Volume II, translated by A.D. Godley, The Loeb Classical Library, Harvard University Press, 1921, 2006, p.150-151, translation modified; Polycrates, tyrant of Samos, ally of Aḥmose II of Egypt, d.522 BC.
In large bodies, the circulation of power must be less vigorous at the extremities... This is the immutable condition, the eternal law of extensive and detached empire.
Edmund Burke, 1774, Letters and Speeches on American Affairs, Everyman, London, 1908, pp.95-96.
Thalassocracy means the rule (κρατεῖν, krateîn, to rule) of the sea (θάλασσα, thálassa, θάλαττα, thálatta, in Attic) -- the coinage for Greek is θάλασσοκρατία, thalassokratía, which is attested in Strabo -- as a verb we see it earlier in Herodotus, in the epigraph above. This does not mean rule by the sea, as "aristocracy" means the rule by the "best," which wouldn't make much sense, but rule by those who control the sea. The first modern systematic discussion of this, although not the use of the term, may have been by Alfred Thayer Mahan in his classic The Influence of Sea Power Upon History, 1660-1783 [1890, Little Brown and Company]. Mahan, however, does not discuss what is usually considered the first thalassocracy attested in its own records, that of Athens in the 5th Century BC.
A thalassocracy is a state that uses its navy to project its power and to unite various possessions that are separated by water. 
Not all naval powers are thalassocracies. Indeed, the key to a state being a thalassocracy is if its power, even its political existence, would collapse completely with the annihilation of its navy. This is the noteworthy fragility of a thalassocracy -- a navy can be crippled or destroyed, sometimes even in a day, leaving the state dismembered and helpless. Mahan's book, by highlighting the importance of sea power, set off a tremendous naval arms race that lasted through World War I, but the competing Powers paid no more attention than Mahan to the fragility of the power they were seeking -- Mahan may have avoided analysis of the Athenian experience just because it ended in failure. Britain, Mahan's own prime exemplar of naval power, managed to lose its "Empire" despite victories in both World War I and World War II. They were Pyrrhic victories; and Britain, as the principal modern thalassocracy, proved to wield a power so fragile that even victory could not preserve it. In fact, Mahan was writing to encourage the United States, which had no particular need of a navy at the time, to build one anyway, as it did.
The first nation whose power depended principally on its ships may have been Crete, about which we known little, and then Phoenicia, about which we know a great deal. Phoenicia, however, was never politically unified, was often under foreign rule, did not effectively retain control of its colonies, and never used colonies as footholds of conquest. The greatest Phoenician colony, Carthage, itself came rather closer to a thalassocracy, retaining control of colonies in the Western Mediterranean and then, under Hamilcar Barca, undertaking the conquest and development of Spain as a Carthaginian imperial possession.
By then a major thalassocracy had already come and gone. In general Greece exhibited the same characteristics as Phoenicia. Greek city states founded colonies but then retained little or no control over them. With Athens, we got something different. The power of Athens began with the League of Delos, a defensive confederation formed to oppose the Persian invasion of Greece in 480. All members made proportional contributions to the common defense, which were kept at the Temple of Apollo on the Island of Delos. Hence the name. With the Persians defeated, the League continued. But the status of Athens as the predominant member began to tell. Pericles wanted to move the Treasury of the League from Delos to Athens. He did this even though no other members of the League agreed. Athens then began spending the money for its own purposes, and the contributions of League members became in effect Tribute paid to Athens. The League became what historians now like to call the "Athenian Empire," although such terminology is pretty anachronistic and inappropriate. Nor is it apt. The "Empire" of Athens, with more or less unwilling participants, depended wholly on the ability of Athens to maintain naval supremacy in the Aegaean Sea. If that were lost or disrupted, Athens would be powerless.
We see in the quote from Herodotus above, who would tell the story of Athenian naval supremacy, that in his judgement it was the Tyrant Polycrates of Samos, Πολυκράτης ὁ Σάμιος (c.538-522) who first tried to "rule the sea," θαλασσοκρατέειν. But this was in an alliance with King Aḥmose II (570-526) of Egypt, who apparently financed a fleet for Polycrates. With his ships, Polycrates began to dominate the Aegaean, and also to spend for monuments and engineering works on Samos (while frightening off Pythagoras, who went into exile, perhaps in 531). This apparently worried Aḥmose, who asked Polycrates to quiet down a bit; but the Persians went for the source of trouble by invading Egypt in 525, shortly after the death of Aḥmose. Polycrates was murdred by the Persians in 522, and then Samos was conquered in 517 -- unable to defend itself without its Egyptian subsidized fleet. This makes a key point in naval history. Navies are expensive. And Athens, with its own commercial wealth, its Laurion silver mine, and the tribute from the League of Delos, needed everything to keep up its naval establishment.
The disruption of its naval power, and the Fall of Athens, is exactly what happened in the war with Sparta, the Peloponnesian War (430-404). Sparta had an invincible army, so the best that Athens could do was avoid it -- relatively easy in a land of peninsulas and islands. If some Spartans could be trapped on an island, 
as did happen (at Sphacteria, on Navarino Bay, in 425), then they could even be defeated and captured. This all worked fine until the Spartans began building their own navy -- something they could not have done, believing in virtuous poverty, and hostile to commercial culture, without being bankrolled by the Persians.
Now Athenian "allies" had an easier time defecting, since they were no longer entirely at the mercy of Athens. The Spartans could now support even island friends. And, if Sparta could wipe out the Athenian fleet in a great battle, it would win the war in one day. The great battle came in 405 at Aegospotami. Destroying the Athenian fleet, the Spartans proceeded at once to the siege of Athens, which surrendered in 404. The Athenian thalassocracy burst like a bubble.
The next state heavily dependent on sea power was, indeed, Carthage. In the First Punic War (264-241) the Romans defeated Carthage and conquered Sicily, in great measure by destroying the Carthaginian fleet. No one would ever say this was done by finesse. The Romans simply filled their ships with soldiers, grappled the Carthaginian ships, dropped gangways, and overwhelmed the enemy with infantry. 
Carthage never regained naval supremacy -- the best moments for Carthage in the First Punic War were when storms destroyed Roman fleets. The response was Hamilcar's, to recreate Carthage as a land power in Spain. Hamilcar's son, Hannibal, then invaded Italy itself in the Second Punic War (218-202). The Romans, unable to defeat Hannibal in open battle, then used their own sea power to defeat him indirectly. Spain was conquered behind him. And then Africa itself was invaded. Hannibal had to abandon his army in Italy and return to defend Carthage itself. There he was finally defeated in battle.
The Romans turned the Mediterranean into their own lake, the Mare Nostrum, "Our Sea." This control, except for some periods of piracy, endured until the Vandals captured Carthage in 439. They then, with exquisite irony, built a fleet that swept the Romans from the Western Mediterranean. When the Visigoths sacked Rome in 410, they came by land, but when the Vandals sacked Rome in 455, they arrived, and left, by boat. This supremacy survived until Belisarius arrived in 534. Their base was abruptly yanked from under the Vandals by the Roman fleet and army from Constantinople. This reestablished Roman maritime control until the 9th century.
At that point two things went wrong. The Arabs, who had conquered the Mediterranean coast from Syria to Spain, and who had already arrived twice by boat to besiege Constantinople (674-677 & 717-718), began asserting naval dominance, resulting in the loss of Roman island possessions, like Crete (823) and Sicily (827-878). Islamic states never organized on the basis of naval supremacy or detached possessions, so there was no real Islamic thalassocracy. The closest may have been by Oman in the Arabian Sea, which projected naval and colonial power all the way to Zanzibar. Otherwise, it is noteworthy that the first possession over which that Caliphate lost control (in 756) was Spain -- the only large conquest separated from the others by water. For the Romans, meanwhile, the other naval challenge was the Vikings, or, as they were called in the East, the Varangians. They arrived at Constantinople, having come down the rivers of Russia, in 839. Several attacks and wars followed, until a Treaty in 988 and the subsequent conversion of Russia to Christianity. Things were improving a bit. A Roman fleet destroyed a fleet of Arab pirates off Provence in 941. This was probably the last great stroke of Roman seapower in the Western Mediterranean. Crete was recovered in 961 and Cyprus in 964. The real end of Roman sea power, however, can be precisely dated. It happened in 1082 when the Emperor Alexius Comnenus signed a commercial agreement with Venice. In short order, the Italian cities, Venice, Pisa, and Genoa in particular, became the great commercial and naval powers of the Mediterranean. Venice countenanced no revival of Roman naval power.
Looking back on the Roman experience, what it looks like is that Rome had a great deal of power apart from its maritime possessions and navy. The Roman Empire, however, was wrapped around the Mediterranean Sea -- as Socrates said, like frogs around a pond. Or like a geode with a hollow in the middle. This meant that naval power was necessary for complete mastery of the area, should there be any other naval power present. Loss of naval predominance might not be fatal, as it was for Athens, but it would be a serious blow to Roman power. Where naval supremacy was lost, as to the Vandals, or in the 9th century, the state was doomed to retreat to a continental redoubt. The Chinese experience is interesting in comparison. The contemporary of the early Roman Empire, the Han Dynasty, broke up (220 AD) and was partially conquered by barbarians, just like Rome. 
China, however, recovered and was reunited by the Sui Dynasty (590), not long after Justinian partially retrieved the Western Empire. China, however, was not wrapped around an empty Sea. China was also culturally, ethnically, and religiously rather more homogeneous. In the Mediterranean world, every little peninsula had a different nationality, different language, and, before Christianity, a different religion. The sort of separatism, manifesting itself in religious dissent, that made Egypt and Syria welcoming of the Arab Conquest, was much more of a danger for Rome than for China. The Roman Empire, even in its Mediaeval incarnation, thus shrank and ultimately collapsed, while China was reconstituted time after time. The disunity of Europe and the Mediterranean world may actually have made for greater cultural and technological innovation. China was historically more conservative. The disunity, however, looks dictated by the geography, and especially by the seas that both separated and connected the lands.
The Italian cities were thalassocracies, but their power remained very limited and could not effectively project itself in continental struggles. They had no effective continental redoubts to speak of. Venice retreated before the Ottomans, and Genoa was successively occupied by France. The rising Great Powers had resources beyond what any Italian city could ever claim. The new Great Powers, however, became tied to naval power with the acquisition of colonial empires. Spain derived much of its power from the silver mines of Mexico and Peru. Every year, Spanish finances hung on the treasure fleet sailing from Vera Cruz to Cadiz. Spain itself, however, did not put its own revenues to use in the development of modern commercial culture and banking. The Netherlands, revolting against Spain (1568-1648), was able to do that. In the 17th century, the new Maritime Powers -- the Netherlands, Britain, and France -- surpassed Spain and Portugal in wealth and power. This had little to do with colonial possessions or even sea power. The European Balance of Power was determined on land, and even all the American silver of Spain could not keep it competitive with the cultural and institutional advantages of its rivals. Britain, as an island, realized how important its navy was, but a purely naval strategy did not begin to tell until well into the 18th century.
British predominance at sea was definitely established in the Seven Years War (1756-1763), when France lost the principal assents of its colonial empire, particularly Canada. This quickly gives us the picture of Britain as the paradigmatic modern thalassocracy. There are already features of this picture, however, that are singularly revealing of both its power and its fragility. The particular power of the British colonial empire was the degree to which British possessions were settled by immigrants and grew into powers in their own right. America was the first in this direction, but then the fate of America reveals a fundamental flaw in the tendency. The American colonies, the originally British ones (not, as it happened, Canada), revolted against Britain. With the help of France and other enemies of Britain, the American Revolution (1776-1783) was successful. This is usually regarded as the end of the "First" British Empire. Just as importantly, it was a grave shock to a British thalassocracy. America ended up, although settled and created from Britain itself, more like the unwilling "allies" of Athens in the League of Delos.
As it happened, British naval dominance was retrieved at the end of the war by victory at the Battle of the Saints in 1782, with which Mahan's original book ends. It did not restore the American colonies. The subsequent French Revolutionary and Napoleonic Eras repeated the experience of the Seven Years War. At the Congress of Vienna, Britain had its pick of strategic colonial possessions, like Malta and South Africa. Subsequently, British dominion rapidly emerged in what were to be the principal classic possessions of the 
British Empire in the 19th century: India, Canada, South Africa, Australia, and New Zealand. To most at the time, and many since, these possessions, and the Royal Navy that united and/or protected them, were the source of the great power of Britain. Marxists even came to think that British Imperialism was the means by which Britain had derailed history and fended off the revolution of the proletariat against capitalism. But Britain was not wealthy because of its empire; and the way in which the empire might have enabled Britain to contend on more equal terms with the rising superpowers of the 20th century was undermined by a characteristic of thalassocracy that had already been revealed in the American Revolution.
Britain was powerful mainly because of (1) commercial culture, though which Britain had risen with the Netherlands, (2) banking, which Britain took over from Amsterdam, creating modern governmental finance through the 
Bank of England in 1694, and (3) the Industrial Revolution. British colonial possessions often began simply by securing (or building) a safe trading station. Cities like Bombay, Singapore, and Hong Kong began in this way. Whether this grew into something more depended on the local conditions, usually whether the hinterland was politically organized enough to control the area and whether this organization was hostile or receptive to British trade and the security of British traders. Thus, African possessions, with small and poorly organized native states in the background, grew into large colonies, while the British presence in China remained confined to a few small outright possessions together with trading privileges, usually extorted by force, from China itself. India fell somewhere in between, as many of the small successor states of the Moghuls were successively acquired, while many other states (the "Princely States") were domesticated with subordinating treaties and close supervision.
Both Imperialist and Marxist opinion was that, since India was a very large and rich place, this is what made Britain rich. There are more and less sophisticated versions of this view. One would be that Britain simply took the wealth of India and transferred it to Britain. Since there weren't exactly cotton mills and battleships in India, this view doesn't hold up too well. Such things were created in Britain, not in India. Nevertheless, even today such a perspective, a sort of Cargo Cult version of economics, is the subtext of many political debates about "natural resources." Marxism itself (as opposed to what Robert Hughes calls recent "lumpen" Marxism, which is of the Cargo Cult sort, what I would call "English Department Marxism") was more sophisticated: Lenin said that Britain needed India as a place to sell production that the British proletariat was too poor to buy, and as an outlet for the "excess capital" that had to be invested somewhere but for which no use could be found in Britain. Unfortunately, as a theory of how the British proletariat became unnaturally content with capitalism, this wasn't very good, since it did not mean, with overproduction sent to India, that the wealth of the British proletariat would increase. The British proletariat would be just as impoverished as before. Also, if British production was being sold to India rather than to domestic consumers, where did Indians get the money to buy it? India, after all, was being "exploited," which should mean that it would become poorer, not richer. Soaking up production from Britain would make it richer. If Lenin's theory of imperialism is going to make any sense, it would have to be that wealth from India is used to enrich and so pacify the proletariat -- but that would not have been consistent with Marxist principles about overproduction and excess capital. There is also the little problem of the matter of fact about where British production and investment actually went. As examined elsewhere, it happens that most British production and investment was either absorbed domestically or exported to (1) other capitalist countries or (2) British immigrant consumers in places like Australia. The largest British trade and investment partner was thus the United States, which had nothing to do with the British Empire and, before World War I, conducted a foreign policy that was often hostile to Britain (strongly encouraged by Anglophobe Irish immigrants).
Britain, therefore, was not rich because of India; and this became painfully evident after Indian independence in 1947, when India failed to develop much economically (with Nehru applying Stalinist economic planning) all the way up through the 1980's and Britain, after the folly of Labour post-war nationalizations and regulation, went on to become richer than ever (although eventually falling behind its own exploited Chinese colony, Hong Kong, in per capita income). More importantly, however, Britain had by then long fallen behind the United States, which covered a continental sized state with immigrant settlement, grew into the largest economy in the world, and saved Britain (and France) from European enemies (i.e. Germany) in World War I and World War II. The American paradigm was, of course, derived from Britain herself. The American colonies of 1776 had simply continued doing, on a larger and larger scale, what they were already doing then. The "Second" British Empire, of the 19th century, continued this kind of thing itself, and also had other continental sized areas, Canada and Australia, to do it in. Why was Britain then not able to keep up?
One problem was simply that other British immigrant colonies never got anywhere near as big as the United States. Even as recently as 2000, the population of the United States was 283 million, the United Kingdom, 59 million, Canada, 31 million, Australia, 19 million, and New Zealand, 4 million. Much of Canada and Australia was simply not as inviting as most of the United States. The other British self-governing "Dominion," South Africa (43 million in 2000), largely consisted of culturally and economically unassimilated Africans. The successful immigrant states, from the United States on, were areas of predominantly thin paleolithic or neolithic tribal settlement. Where British settlement was attempted in areas of larger, more organized, and more advanced (usually iron age) populations, as in South Africa or Rhodesia, a demographic and cultural predominance of immigrants was not achieved. Nothing of the sort could even be attempted in India, where the entire population of Britain could have been lost among the natives -- whose own memories were easily of the firearms and Empire of the Moghuls.
A large population, of course, does not translate directly into wealth or power, or India and China never would have been poor or weak. What counts is a population that is culturally entrepreneurial and industrious. Immigrants to the United States were preferentially of such populations. With such people, production increases, which means that 283 million Americans are going to vastly outproduce 113 million Britons, Canadians, Australians, and New Zealanders. Indeed, the Gross Domestic Product of the United States in 2000, adjusted for purchasing power, was 9.8 trillion dollars, while that of the others combined was 2.5 trillion -- 25.8% (with China just at a trillion and India less than half that). The day of reckoning for the difference came in World War I, when Britain simply ran out of money for the war -- something that had been unthinkable at least since the War of the Spanish Succession (1701-1713). [note]
More than just relative size, however, was the problem peculiar to a thalassocracy. British possessions were never politically integrated into the home country and saw themselves increasingly as distinct --politically, economically, and culturally -- from the Mother Country. The lesson that Britain took from the American Revolution was not that colonies should be given political power commensurate with their importance in a central government, but that they should be allowed enough self-rule to keep them happy. This gradually became complete self-rule for the Dominions, and finally virtual independence, confirmed with the Statute of Westminster in 1931. This division not only sometimes created conflicting political purposes but also introduced commercial diseconomies, since territories with self-rule began even in the 19th century to prefer protective tariffs. With the Depression, even Britain abandoned free trade. Since protective tariffs are a negative sum game, i.e. total value decreases rather than increases, the British Commonwealth ended up as an economic organization much worse off than the United States, which contained within itself what was in effect a colossal free trade zone.
The physical detachment of British possessions from Britain created a centrifugal tendency towards distinct identity and interest that was fatal to British thalassocracy all the way from the American Revolution to World War II. Unlike Athens, Britain did not need to rely on "allies" forcefully incorporated into its system. Unlike Rome, Britain did not need to create a super-identity overlaying older historically and culturally distinct communities that it had conquered (though something of the sort was tried in India and other purely imperial acquisitions). No, in America and elsewhere, it had its worst problems with English speaking immigrants who became divided in identity and interest from the Mother Country. When Britain lost its predominance at sea, in World War I and World War II, albeit to a fraternal ally, the United States, the British "Empire" was a bubble that burst as decisively as did that of Athens -- although leaving a symbolic and sentimental structure, the British Commonwealth, behind. The symbolic and sentimental, however, does not translate into geopolitical force, and Britain lapsed into the second rank of Powers. A key year in that respect was 1967, when Britain withdrew from all its traditional strategic commitments East of Suez. It was on the verge of retiring the aircraft carriers that gave the Royal Navy any remote strike capability when Argentina invaded the Falklands in 1982. If the Argentines had just waited a couple of years, Britain would have had grave difficulty mounting an effective naval response.
Meanwhile, the Age of the Superpowers had arrived, initially meaning the United States and the Soviet Union. The power of the Soviet Union, although credibly based on a continental mass and a large population, turned out to be largely founded on bluff. The regime actively suppressed the commercial culture and economic institutions that could have made it a real competitor with the United States and the European democracies. While the Soviet Union collapsed in 1991, the European Community was trying, through economic integration, to achieve equality with the United States -- a project extended in the 90's into an actual "European Union." But it is handicapped by a controlling and bureaucratic mentality, with socialist purposes, that sometimes rises nearly to Sovietizing levels. China, although allowing hardly a spark of democracy, nevertheless seems rather more aware of what it needs to do economically.
Ideological objections to the United States, as a "neo-colonialist" or "neo-imperialist" power, still rest on the Cargo Cult or Marxist misconceptions already mentioned. The United States uses its sea power in one of the ways that Britain did, to secure the seas for shipping and to promote the political stability that is favorable to trade. Objections to this, if not mere envy, will usually dismiss trade as either unnecessary or a positive evil. The poverty of the countries presumptively "exploited" by the United States is attributed, if not by standard Marxist analysis to alienated labor, etc., then most commonly by the Cargo Cult explanation to the notion that in international trade countries are denied the true value (the Mediaeval "just price") of their own "natural resources." Hence, African countries are poor because they don't get paid enough for the materials they mine and export.
Unfortunately for these views, there has been an international oil cartel for many years now, OPEC (the Organization of Petroleum Exporting Countries), whose entire purpose is to drive up oil prices through price fixing and other monopoly practices that are usually regarded as diabolical when used by private businesses in any country. OPEC has been relatively ineffective for two reasons: (1) The natural working of supply and demand, which determines free market prices, tends to overcome price fixing, since OPEC members are tempted to cheat on each other, and OPEC has no enforcement powers to prevent this. (2) Even the monopoly rents sought by OPEC members, like Spanish silver, do not translate into genuine economic development in their countries, something that requires the entrepreneurial population and legal and financial institutions that those with oil wealth tend to regard as unnecessary or undesirable. Thus, even the wealthiest of the oil states, like Saudi Arabia, have high unemployment [note] and the sort of restless and ideologized malcontents, with not much to do, who figure that they are just not getting paid "enough" for what is rightfully theirs. Even worse, we find the phenomenon of someone like the millionaire Osama ben Laden, who apparently would like to force everyone to live in Mediaeval ascetic poverty, while using his wealth to destroy, with some of its own weapons, the religious enemy manifest in the power of the West.
The dynamic of world history, consequently, has left behind the last thalassocracy. But this may not be the end of the phenomenon. It is hard to imagine that human colonization will not someday extend out into the solar system, although so far it is has been surprisingly delayed well beyond the introduction of space travel. When such colonization does develop, the conditions characteristic of thalassocracy will return. Communication, indeed, will be no problem between extraterrestrial human colonies, but travel will be another matter. Getting to Mars by spaceship for some time to come will be not unlike getting to Australia by sailing ship. It took Columbus a month to get across the Atlantic, but that is not enough to get anywhere in the solar system beyond the Moon. Indeed, technological innovations can make such travel easier. Mars may be weeks rather than months away with ion engines. But all this does is move outward the boundary of what is conveniently accessible. 
Even communication will become problematic in one sense, because the limitation of the velocity of light will render convenient dialogue impossible. Out at Jupiter or Saturn, the round trip for a message to Earth will be measured, not in seconds or even minutes, but in hours. Distance and awkwardness, at least, of communication will render remote colonies, once they become populous and self-sustaining, liable to the same dynamic of distinct identity and interest, not to mention the same limitations of military control, that inevitably fragmented the British thalassocracy. An exploration of this theme in science fiction, with a human colony as close as the Moon, can be found in 
Robert Heinlein's The Moon is a Harsh Mistress [1966], where the Moon in 2076 successfully revolts against the Earth. As the Earth itself seems to be moving towards ever more centralized political control, even in the democracies, with devices of police state control expanding, it may prove to be the greatest hope for human freedom and flourishing that there will be Americas and Australias of the future beyond effective political control on all the thousands of hunks of rock in the Solar System, if not beyond. Light speed or instantaneous transportation might overcome that barrier, but, again, all it will do is push out the boundary. 
The stars, if not the asteroids, will always be there, with refuge for any future Mayflower. The fragility of a thalassocracy thus, as it happens, may be the very best thing about it.
Robert Heinlein (1907-1988), The Libertarian in the Lifeboat
World War I also revealed the fragility of thalassocracy in another way. The British Navy was fully aware that while Germany would not lose the war even with a devastating naval defeat, it could win the war with a devastating victory. The Battle of Jutland in 1916 was something that could easily have been the British Aegospotami. If the British Grand Fleet were crippled or destroyed, the German Navy could have cut off Britian from food and arms imports, stranded the British Army in France, and devastated British cities. This being the case, German actions show extreme ignorance and foolishness. It it is as though the Germans hadn't quite thought through what their Navy was for, or what the strategic situation was. Except for Jutland, from which the German fleet only tried to escape, there was no other general fleet action in the War, even though the Germans had nothing to lose (except face, and a few thousand men -- no more lives than were thrown away every few days in the trenches) and everything to gain.
After Jutland, the Germans even knew from direct experience that their ships were very well built, tough, and could take tremendous punishment (British 15-inch shells) without sinking -- while three British battlecruisers had simply blown up and sunk with all hands. This didn't make any difference. When the War was obviously lost in 1918, the Kaiser finally instructed the High Seas Fleet to sail out in a final, desperate attack. It was way too late. The British fleet by then was not only larger by its own construction, but was reinforced with American battleships. But the attack never happened because the German sailors mutinied. They were not going to throw away their lives in a lost cause.
By the way, although the British thought they had a pretty good idea why their ships had sunk so catastrophically, there is no certainty that they had found all the problems. A new class of battlecruisers was designed with the "lessons of Jutland" in mind. Of the new ships, only the great Hood was completed. As it happened, the Hood, like its Jutland predecessors, blew up and sank with all hands when hit by the German battleship Bismarck in 1941. Exactly why the Hood sank is still a mystery, though now it has become possible to locate sunken ships in the deep ocean (like the Bismarck itself) and minutely examine the wrecks.
The thought seems to be now that, although the British battlecruisers could have had better protection, the catastrophic explosions on the ships meant that the magazines, which had the best protection, had detonated. This occurred not because of construction failures, but because of discipline failures. Crews left open the blast doors between the turrets and the magazines so that ordinance could be brought up faster and the guns could be worked faster. When German shells penetrated the turrets (from insufficient protection), the blast went right down to the magazines. The best evidence for this is that the same catastrophe nearly happened on the battlecruiser Lion, which was the flagship of Admiral Beatty. A turret was hit by a German shell, which set off a fire that eventually cooked off the amunition in the turret. The blast killed the whole crew. However, one man, badly burned and dying, Royal Marine Major Francis Harvey, nevertheless had been able to close the blast doors and flood the magazine. The ship was saved, as was the life of Admiral Beatty himself.
We don't know, and may never know, if the indiscipline in the turrets, apparently encouraged by Beatty, was the kind of thing later responsible for the loss of the Hood.