The other side of the hill. Espionage has never been so discredited. The heroic myths of the Second World War have given way to the cynical belief that spooks are just the servants of politicians. But has intelligence ever been as crucial as we thought?

Intelligence in War: knowledge of the enemy from Napoleon to al-Qaeda

John Keegan <em>Hutchinson,

Boring British experience of the year? I nominate mentioning "military intelligence" in a crowded room, and hearing all those jolly voices shouting: "Oxymoron!" Was there ever a time when the intelligence profession and its products were so derided? Iraq and the Hutton inquiry brought this mockery to a new pitch. The spooks in Britain and America seemed to have got everything wrong - both their "strategic intelligence" about how the Iraqis and their regime would react to being invaded and their "tactical", real-time intelligence about where their leaders or semi-mythical weapons were at a given moment. Worse still, they let their political customers deform their meagre results and get them even more wrong.

John Keegan, who completed this book before the inquiry began, suggests deeper grounds for all this mockery. Intelligence, he argues, had become wildly overestimated for two reasons: because the cold war allowed the public to confuse military, operational intelligence with espionage, and because the heroic myths of the Second World War confused operational intelligence with subversion. But these bubbles of glory were certain to burst in the anti-heroic climate of the past few years, and Keegan is now determined to replace them with a sober diagram. His book is not about spies or sabotage. Its subject is military intelligence - the attempts of commanders through history to find out what is happening on the other side of the hill.

In the best Sandhurst manner, he breaks down military intelligence into five stages: "acquisition" by human intelligence ("humint"), signals intelligence ("sigint") or visual survey (from Admiral Nelson's telescope to satellite or radar screen); "delivery" (getting the information through); "acceptance"(establishing the credibility of the source); "interpretation" (fitting the jigsaw together); and finally "implementation" (convincing the decision-makers to act on the information). The weakness of this schema is that it treats intelligence work as autonomous. Iraq has reminded us, painfully enough, that intelligence is part of a wider political context, in which the political masters often decide what they want to do and only then invite their intelligence services to find the evidence that justifies it.

Keegan describes seven campaigns or war episodes in which intelligence played an important part. Important - or decisive? Here we come quickly to his real theme: how useful is intelligence in war? And his answer, repeated over and over again as he examines his evidence, is that it can be immensely useful and important, but is almost never decisive. In the end, it is not knowledge that wins battles but force. "War is ultimately about doing, not thinking." An ill-informed general or admiral can defeat an adversary who holds all the knowledge cards, if he knows how to fight and if his men have more courage.

A lot of this book is about wars rather than intelligence. But John Keegan, military historian and defence correspondent, writes so well that this does not matter much. His narratives of Thomas "Stonewall" Jackson's 1862 campaign in the Shenandoah Valley, or of Nelson's desperate search across the Mediterranean for the French fleet in 1798, or of the battle for Crete in 1941, are all unforgettably well told. So is his account of how signalling technology evolved, from the days of searching empty horizons for topmasts through the ages of wireless and then of code-breaking "sigint" and on to the return of the visual in the form of photographic intelligence and satellites. (Keegan has never been one of those nerdish "toys for the boys" war historians. He reminds his readers constantly that these esoteric games sent human beings to their deaths, in terror and pain and often unnecessarily.)

The case of Crete is central to Keegan's argument. This is the extreme example of knowledge not being enough. Bernard Freyberg, commanding the island's defenders, had more troops than the German attackers. He also had intelligence from Ultra, the great code-breaking operation at Bletchley, which read German signals encrypted by the Enigma machine. In Crete, Ultra managed to provide him with a version of the full German invasion plan. Freyberg knew exactly when the attackers would arrive, that they would be parachutists supported by glider-borne infantry, and that they would land on Crete's three airfields. As Keegan writes, it was "one of the most complete pieces of timely information ever to fall into the hands of an enemy". And yet Freyberg lost. He annihilated the attackers at two airfields, but at Maleme the Germans hung on to a corner of the runway until reinforcements arrived, and eventually broke out. Once they had done so, Luftwaffe air supremacy made German victory inevitable.

Keegan suggests several reasons for the disaster. Freyberg, misunderstanding earlier signals, thought there would also be a seaborne landing and divided his forces. More seriously, the Ultra material did not tell him that Maleme was the primary German objective, or which units would land where. What Freyberg got was a Bletchley-made resume of the original Enigma signal, not the admittedly complex and confusing raw material. Keegan suspects that the code-breakers did receive those crucial details but decided not to pass them on. (We can't know, because the original decrypts are still secret 62 years later.)

And yet Keegan believes that something simpler mattered more - the terrible, superhuman courage of the German attackers, crash-landing aircraft after aircraft under murderous close-range fire. The New Zealand defenders at Maleme were brave, but not suicidal. Freyberg knew a lot, but he did not know that Maleme would be the do-or-die battle for all Crete. The Germans did, and they won.

The Battle of Midway, in 1942, seems at first sight to be a conclusive example of how superior intelligence wins battles. The Americans intercepted and shattered a Japanese battle fleet heading towards the Hawaiian archipelago. Their triumph was preceded by dazzling feats of decryption and interpretation of Japanese naval signals, providing an accurate outline of the enemy plan down to the time and place at which the Japanese carriers would launch their aircraft against Midway Island. But Keegan reveals that, on the day, luck counted for more than knowledge. The main American attack squadrons failed to find the enemy. The Japanese were about to start their own onslaught when pure chance - their fighter escort at the wrong height, the tell-tale wake of a destroyer - allowed a group of American dive-bombers to find them and attack unopposed. Three out of the four carriers were sunk in five minutes, the fourth a few hours later. As Keegan concludes, the American admirals had the enemy's plans "laid clear before them, or as clear as the obscurities of war will ever allow. They had, all the same, nearly lost."

The book grows less convincing as it approaches the present. Keegan, whose views of history are conventionally conservative, rightly highlights the British fascination with covert partisan operations, in which British officers lead "native" irregulars, and shows how Winston Churchill's instruction to the Special Operations Executive in 1940 to "set Europe ablaze" dated back to his romantic admiration for the Boers and even for the IRA of Michael Collins's day. But Keegan's recipe for penetrating al-Qaeda is just as romantic: the recruitment of "brave individuals, fluent in difficult languages and able to pass as native members of other cultures". Here the old nut-juice bottle is being uncorked and the contents applied to that turbaned figure with the curiously blue eyes in the bazaar. Keegan, who is certain that Saddam Hussein's "weapons of mass destruction" have merely been hidden, also insists that there is indeed a "historic war" between the "crusaders" and the Islamic world, and proclaims (without evidence) that illegal immigrants in the west are the recruiting pool for anti-western terrorism. He may be right that "war is ultimately about doing, not thinking". But why can he not see that war in our times, a doing which acts first and invents its thinking afterwards, achieves nothing more than the assurance of other wars in the future?

Neal Ascherson's most recent book is Stone Voices (Granta)