Thirteen months ago, the United States sent Navy ships toward Syria as it prepared to launch strikes against President Bashar al-Assad’s regime following its use of chemical weapons. Four destroyers carrying about three dozen Tomahawk missiles each made up the bulk of the force, but the Pentagon also could have launched airstrikes from bases in Turkey or Europe or submarines that quietly patrol the sea.

President Obama backed off hitting Assad’s regime then, saying he wanted Congress to vote on the plan. Two weeks later on Sept. 14, 2013, Russia and the United States agreed to a deal that allowed Syria’s declared chemical weapons to be destroyed at sea this summer by a U.S. crew on the MV Cape Ray, a container ship specifically outfitted for the mission.

The aborted Syria strikes last year are instructive in considering the options at the Pentagon’s disposal now, as Obama prepares for a speech Wednesday night in which he is expected to make the case for expanding action against the Islamic State. The militant group has taken control of portions of both Syria and Iraq, seized weapons from both Syrian and Iraqi government forces and killed hundreds of civilians, if not more, across the two countries.

The strikes in Syria under consideration could be launched from a number of bases in the Persian Gulf from which the United States is operating to hit Islamic State targets in Iraq. U.S. military officials have not identified those bases, citing diplomatic sensitivities with the countries involved. But they likely include al Udeid Air Base in Qatar, Ali al Salem Air Base in Kuwait and al Dhafra Air Base in the United Arab Emirates, as this Washington Post story last month outlined. Predator drones and other U.S. aircraft also are likely flying from Incirlik Air Base in Turkey, and the U.S. military also visits Jordanian bases on occasion.

The U.S. has carried out an average of five airstrikes a day  in Iraq over the last month, setting an operational framework for how the mission could be expanded into Syria. But Syria’s closer proximity to the Mediterranean Sea may provie some other options, including fighter jets or AC-130 gunship planes taking off from military bases in Europe.

In addition, the U.S. Navy has a number of ships in the region, a Navy official said. If Tomahawk missile strikes are used this time, they could be launched from the USS Cole, a destroyer currently in the Mediterranean. Fore operations in Iraq, the United States also continues to fly planes from the USS George H.W. Bush, an aircraft carrier in the Persian Gulf.

U.S. military action in Syria could raise complicated issues with the government in Damascus. Assad’s regime warned last month that the United States should not carry out airstrikes in Syria without the consent of the Syrian authorities.

Syria’s military is also using its air force to target the Islamic State, a campaign that accelerated last month as the militant group won a series of victories in northern Syria’s Raqqah province. The militants stormed the Tabqa airfield, and may have seized a number of shoulder-fired surface-to-air missiles.