Military officials said it was never intended to be the leading edge of a broader campaign to dislodge Mr. Assad from power, or force a political settlement in a country that has been ripped apart by six years of a bloody civil war.<\/p>\n The question for the Pentagon, however, is whether this 21st-century equivalent of a shot across the bow will ensure that poisonous gas will no longer be among the many scourges that plague Syria, or whether it will gradually draw the United States in a multisided military tug of war over the future of the Syrian state.<\/p>\n If there is one description that summed up the plan, which was developed at the headquarters of the United States Central Command in Tampa, Fla., it is \u201cproportional.\u201d Details of the plan were described to reporters at a briefing on Friday by senior military officials who spoke on the condition of anonymity in accordance with Pentagon protocol.<\/p>\n<\/div>\n<\/div>\n The Americans wanted to send a specific signal by striking only the airfield that a Syrian Su-22 warplane had used for its mission on Tuesday to drop a chemical bomb in the middle of the town of Khan Sheikhoun, in southern Idlib Province.<\/p>\n Before the American attack could go forward, however, American intelligence officials had to satisfy senior commanders \u2014 and, presumably, President Trump \u2014 that it had the culprit. The evidence was abundant, and American intelligence analysts concluded they had \u201chigh confidence\u201d in their assessments.<\/p>\n The Americans had tracked the Syrian jet as it took off from the Al Shayrat airfield and dropped a bomb in the middle of a street. The time of the chemical attack, just before 7 a.m., correlated with reports that residents were exhibiting signs of having been subjected to nerve agent. The crater from the bomb showed staining that experts associated with a shell filled with chemical agents.<\/p>\n American intelligence officials also suspect that an attempt might have been made to frustrate efforts to gather evidence of a chemical assault. After victims were rushed to a hospital, a small drone appeared overhead before disappearing. About five hours later, the drone returned and another airstrike hit the medical center; American officials do not know if the drone or the second strike was launched by Syria or Russia.<\/p>\n The shifting fortunes on the battlefield may explain why the Assad government mounted its largest chemical weapons attack since August 2013. In recent weeks, rebel forces have pushed to connect the areas they controlled in Hama and Idlib Provinces. The Syrian government\u2019s control of the Hama airfield was at risk; it was being used by the Assad government as a helicopter base and, it is suspected, as a factory for some of the barrel bombs Syria\u2019s forces had used to deadly effect.<\/p>\n American military officials say they do not believe the strike on Tuesday, which they said was carried out with a nerve agent, was necessarily unique. On March 30, panicky Syrian forces may have used a similar nerve agent in Hama Province, though American officials said they lacked forensic evidence to prove it. On March 25, the Syrians also mounted an attack using chlorine; its use in war is illegal under an international convention banning chemical weapons.<\/p>\n Having concluded that chemical weapons were used by Syrian forces, the next challenge for the Trump administration was to settle on a response. The military options were developed on Wednesday, and when they were narrowed down, the Al Shayrat airfield was in the cross hairs.<\/p>\n Equipped with bunkers for storing chemical munitions, the airfield had been built as a potential launching pad for attacks with chemical weapons \u2014 weapons that Mr. Assad was supposed to have given up as part of an agreement that was worked out by the United States and Russia.<\/p>\n![\"\"](\"https:\/\/static01.nyt.com\/images\/2017\/04\/08\/world\/08Military\/08Military-master768.jpg\")
WASHINGTON \u2014 The American cruise-missile strike that destroyed at least 20 warplanes in Syria<\/a> on Friday was devised by American war planners as a one-time operation to deter President Bashar al-Assad<\/a> from using his secret stockpile of chemicals ever again.<\/p>\n