The Wall Street Journal reports: As Syrian troops battled rebel forces in the Damascus suburbs Aug. 18, U.S. eavesdropping equipment began picking up ominous signals.

A special Syrian unit that handles chemical weapons was ordered closer to the front lines, officials briefed on the intelligence say, and started mixing poisons. For two days, warning signs mounted until coded messages went out for the elite team to bring in the “big ones” and put on gas masks.

U.S. intelligence agencies didn’t translate the intercepts into English right away, so White House officials didn’t know what the Syrian regime was planning until the assault began. Just before 2:30 a.m. on Aug. 21, the first salvo of poison-filled rockets streaked through the clear night sky and crashed into rebel strongholds.

Sarin gas, which kills almost instantly by attacking the nervous system, spread across sleeping farms. Pushed down by falling temperatures, the poison settled in low-lying areas and penetrated homes.

Men, women and children began coughing and gagging, with little more than wet handkerchiefs and T-shirts to hold over their mouths. Neighborhood doctors quickly ran out of antitoxins, and, in a desperate effort to wash away the poison, flooded clinic floors and dragged unconscious victims through the water. More than 1,400 people died, according to U.S. estimates, making it the worst chemical-weapons strike in a quarter century.

A final report is due soon from the United Nations. The Wall Street Journal has pieced together a reconstruction of that fateful day from battlefield reports and dozens of interviews with eyewitnesses, rebels, medics, activists and Western intelligence officials. It reveals both the horror of the attack and the months of miscalculations by the Syrian regime, opposition groups and U.S. government that left them all unprepared for what happened.

U.S. and Israeli communications intercepts reveal chaos inside the Syrian regime that night. When the reports of mass casualties filtered back from the field, according to the officials briefed on the intelligence, panicked Syrian commanders shot messages to the front line: Stop using the chemicals!

Calls came in to the presidential palace from Syrian allies Russia and Iran, as well as from Hezbollah, the Lebanese militant group whose fighters were inadvertently caught up in the gassing, according to previously undisclosed intelligence gathered by U.S., European and Middle Eastern spy agencies. The callers told the Syrians that the attack was a blunder that could have profound international repercussions, U.S. officials say.

The Obama administration had been closely monitoring Syria’s chemical-weapons stockpile since the conflict began in 2011, and had watched the regime carry out about a dozen small-scale chemical attacks before the big one, U.S. officials say. Even if they had translated the intercepts before the Aug. 21 strike, these officials say, they likely wouldn’t have acted because there were no indications it would be out of the ordinary.

Top policy makers had little appetite for getting more deeply involved in the conflict, and questions loomed large about the legality of providing support to the rebels and the best strategy for managing the chemical-weapons threat, these officials say. Rebel leaders and their allies in the U.S. government say the White House failed to act on requests for gas masks, antidote injectors and other protective gear until it was too late.

All told, the events of Aug. 21 changed the Middle East and U.S. policy in ways likely to reverberate for years. It prompted the U.S. to consider and then pull back from military action. The eventual deal to avert a strike, in which Syria agreed to destroy its chemical-weapons stockpiles, elevated Russia, for now, to a leadership position in the region.

President Bashar al-Assad has tightened his hold on power. His regime has denied using chemical weapons, blaming the attacks on the rebels. In exchange for giving up his chemical arsenal, he avoided an American military intervention and likely will get even more support from Russia and Iran. Mr. Assad has pressed ahead with his offensive using conventional arms. U.S. intercepts show a Russian official later boasting to a Syrian counterpart about how easy it had been to get the U.S. to back off strike plans, officials briefed on the intelligence say.

Syrian opposition leaders made their first formal appeal to the U.S. for protection from chemical weapons back in June 2012. At a meeting in Washington, opposition representatives handed administration officials a request for various nonlethal supplies, including 2,500 gas masks, say people who attended.

Samantha Power, then the White House’s top human-rights official and now U.S. ambassador to the United Nations, was receptive, these people say. But other White House advisers, they say, questioned whether the masks would make much of a difference. Some worried that if Islamic extremists in the opposition got their hands on them they might try to seize poison gas from the regime. Administrative lawyers worried about potentially running afoul of domestic and international law.

“It was never ‘no.'” says one opposition representative about what would become a series of requests. “But it would never happen.”

A senior administration official says, “Decisions that were made on assistance to the opposition were made in consultation with them as to what their priorities were.”

That July, American and Israeli spy agencies for the first time intercepted fragmentary intelligence about regime forces using chemical weapons on a small scale. The evidence wasn’t conclusive—there were no physical traces—but some top military officials say they found it persuasive and wanted to make it clear right away to Syria the U.S. wouldn’t tolerate even small attacks.

Then-White House Deputy National Security Adviser Denis McDonough and other officials told their agency counterparts that the top-secret information shouldn’t be made public, but congressional committees were briefed, according to officials. Mr. McDonough also decided to restrict the distribution of such “raw” intelligence inside the government because of its sensitivity, these people say. White House officials didn’t want to set off a chain reaction that would restrict their ability to decide how active a role to play, senior U.S. officials say.

The following month, on Aug. 20, President Barack Obama said the regime would cross the U.S.’s “red line” if it started moving or using “a whole bunch of chemical weapons.”

Last December, the U.S. intercepted an unusually complete communication in which Syrian officials spoke about a potentially larger-scale chemical attack involving aircraft. The White House sent private messages to the Russian government, which in turn asked Iran to lean on the Syrians to scrap the plan, according to current and former U.S. officials involved in the matter. Iran did just that, the officials say. A spokesperson for Iran’s U.N. mission said Iran had made it clear it opposed the use of chemical weapons. [Continue reading…]