Robert Fisk: He takes his secrets to the grave. Our complicity dies with him

We've shut him up. The moment Saddam's hooded executioner pulled the lever of the trapdoor in Baghdad yesterday morning, Washington's secrets were safe. The shameless, outrageous, covert military support which the United States - and Britain - gave to Saddam for more than a decade remains the one terrible story which our presidents and prime ministers do not want the world to remember. And now Saddam, who knew the full extent of that Western support - given to him while he was perpetrating some of the worst atrocities since the Second World War - is dead.

Gone is the man who personally received the CIA's help in destroying the Iraqi communist party. After Saddam seized power, US intelligence gave his minions the home addresses of communists in Baghdad and other cities in an effort to destroy the Soviet Union's influence in Iraq. Saddam's mukhabarat visited every home, arrested the occupants and their families, and butchered the lot. Public hanging was for plotters; the communists, their wives and children, were given special treatment - extreme torture before execution at Abu Ghraib.

There is growing evidence across the Arab world that Saddam held a series of meetings with senior American officials prior to his invasion of Iran in 1980 - both he and the US administration believed that the Islamic Republic would collapse if Saddam sent his legions across the border - and the Pentagon was instructed to assist Iraq's military machine by providing intelligence on the Iranian order of battle. One frosty day in 1987, not far from Cologne, I met the German arms dealer who initiated those first direct contacts between Washington and Baghdad - at America's request.

"Mr Fisk... at the very beginning of the war, in September of 1980, I was invited to go to the Pentagon," he said. "There I was handed the very latest US satellite photographs of the Iranian front lines. You could see everything on the pictures. There were the Iranian gun emplacements in Abadan and behind Khorramshahr, the lines of trenches on the eastern side of the Karun river, the tank revetments - thousands of them - all the way up the Iranian side of the border towards Kurdistan. No army could want more than this. And I travelled with these maps from Washington by air to Frankfurt and from Frankfurt on Iraqi Airways straight to Baghdad. The Iraqis were very, very grateful!"

I was with Saddam's forward commandos at the time, under Iranian shellfire, noting how the Iraqi forces aligned their artillery positions far back from the battle front with detailed maps of the Iranian lines. Their shelling against Iran outside Basra allowed the first Iraqi tanks to cross the Karun within a week. The commander of that tank unit cheerfully refused to tell me how he had managed to choose the one river crossing undefended by Iranian armour. Two years ago, we met again, in Amman and his junior officers called him "General" - the rank awarded him by Saddam after that tank attack east of Basra, courtesy of Washington's intelligence information.

Iran's official history of the eight-year war with Iraq states that Saddam first used chemical weapons against it on 13 January 1981. AP's correspondent in Baghdad, Mohamed Salaam, was taken to see the scene of an Iraqi military victory east of Basra. "We started counting - we walked miles and miles in this fucking desert, just counting," he said. "We got to 700 and got muddled and had to start counting again ... The Iraqis had used, for the first time, a combination - the nerve gas would paralyse their bodies ... the mustard gas would drown them in their own lungs. That's why they spat blood."

At the time, the Iranians claimed that this terrible cocktail had been given to Saddam by the US. Washington denied this. But the Iranians were right. The lengthy negotiations which led to America's complicity in this atrocity remain secret - Donald Rumsfeld was one of President Ronald Reagan's point-men at this period - although Saddam undoubtedly knew every detail. But a largely unreported document, "United States Chemical and Biological Warfare-related Dual-use exports to Iraq and their possible impact on the Health Consequences of the Persian Gulf War", stated that prior to 1985 and afterwards, US companies had sent government-approved shipments of biological agents to Iraq. These included Bacillus anthracis, which produces anthrax, andEscherichia coli (E. coli). That Senate report concluded that: "The United States provided the Government of Iraq with 'dual use' licensed materials which assisted in the development of Iraqi chemical, biological and missile-systems programs, including ... chemical warfare agent production facility plant and technical drawings, chemical warfare filling equipment."

Nor was the Pentagon unaware of the extent of Iraqi use of chemical weapons. In 1988, for example, Saddam gave his personal permission for Lt-Col Rick Francona, a US defence intelligence officer - one of 60 American officers who were secretly providing members of the Iraqi general staff with detailed information on Iranian deployments, tactical planning and bomb damage assessments - to visit the Fao peninsula after Iraqi forces had recaptured the town from the Iranians. He reported back to Washington that the Iraqis had used chemical weapons to achieve their victory. The senior defence intelligence officer at the time, Col Walter Lang, later said that the use of gas on the battlefield by the Iraqis "was not a matter of deep strategic concern".

I saw the results, however. On a long military hospital train back to Tehran from the battle front, I found hundreds of Iranian soldiers coughing blood and mucus from their lungs - the very carriages stank so much of gas that I had to open the windows - and their arms and faces were covered with boils. Later, new bubbles of skin appeared on top of their original boils. Many were fearfully burnt. These same gases were later used on the Kurds of Halabja. No wonder that Saddam was primarily tried in Baghdad for the slaughter of Shia villagers, not for his war crimes against Iran.

We still don't know - and with Saddam's execution we will probably never know - the extent of US credits to Iraq, which began in 1982. The initial tranche, the sum of which was spent on the purchase of American weapons from Jordan and Kuwait, came to $300m. By 1987, Saddam was being promised $1bn in credit. By 1990, just before Saddam's invasion of Kuwait, annual trade between Iraq and the US had grown to $3.5bn a year. Pressed by Saddam's foreign minister, Tariq Aziz, to continue US credits, James Baker then Secretary of State, but the same James Baker who has just produced a report intended to drag George Bush from the catastrophe of present- day Iraq - pushed for new guarantees worth $1bn from the US.

In 1989, Britain, which had been giving its own covert military assistance to Saddam guaranteed ?250m to Iraq shortly after the arrest of Observer journalist Farzad Bazoft in Baghdad. Bazoft, who had been investigating an explosion at a factory at Hilla which was using the very chemical components sent by the US, was later hanged. Within a month of Bazoft's arrest William Waldegrave, then a Foreign Office minister, said: "I doubt if there is any future market of such a scale anywhere where the UK is potentially so well-placed if we play our diplomatic hand correctly... A few more Bazofts or another bout of internal oppression would make it more difficult."

Even more repulsive were the remarks of the then Deputy Prime Minister, Geoffrey Howe, on relaxing controls on British arms sales to Iraq. He kept this secret, he wrote, because "it would look very cynical if, so soon after expressing outrage about the treatment of the Kurds, we adopt a more flexible approach to arms sales".

Saddam knew, too, the secrets of the attack on the USS Stark when, on 17 May 1987, an Iraqi jet launched a missile attack on the American frigate, killing more than a sixth of the crew and almost sinking the vessel. The US accepted Saddam's excuse that the ship was mistaken for an Iranian vessel and allowed Saddam to refuse their request to interview the Iraqi pilot.

The whole truth died with Saddam Hussein in the Baghdad execution chamber yesterday. Many in Washington and London must have sighed with relief that the old man had been silenced for ever.

'The Great War for Civilisation: The Conquest of the Middle East' by Robert Fisk is now available in paperback