For nearly two weeks, the United States has signaled that it would strike at militant targets in Syria as part of an expanded military campaign against the Islamic State militant group. Degrading and eventually destroying the group is part of a “comprehensive and sustained counterterrorism strategy,” President Obama said Sept. 10 in a nationally televised address at the White House.

“I have made it clear that we will hunt down terrorists who threaten our country, wherever they are. That means I will not hesitate to take action against ISIL in Syria, as well as Iraq,” Obama said, using one of the acronyms for the radical Islamist group. “This is a core principle of my presidency: If you threaten America, you will find no safe haven.”

U.S. forces have continued to strike the militants in Iraq since then, dropping bombs and firing missiles a couple of times virtually every single day. But the United States didn’t strike in Syria until early Tuesday local time (Monday night in Washington), when it delivered a heavy bombardment on numerous sites. There were 22 military strikes in all, involving not only aircraft from the United States and partner nations, but 47 Tomahawk cruise missiles delivered from Navy ships in the Persian Gulf and Red Sea.

All told, it was likely the single largest day for the U.S. military in terms of ordnance dropped since the opening salvos of its 2011 campaign in Libya, when both airstrikes and scores of Tomahawk missile strikes were used to target the forces of Libyan leader Moammar Gaddafi.

The U.S. Navy released video Tuesday of troops launching Tomahawk cruise missiles against Islamic State militants in Syria. (Video courtesy U.S. Navy)

With the large-scale action, the United States effectively signaled that its military campaign against militants in Iraq and Syria has entered a new phase. It also came as the Pentagon expanded the scope of its targets in the campaign beyond the Islamic State: the strikes also hit the Khorasan Group, a shadowy affiliate of al-Qaeda that is said to include foreign fighters from Afghanistan, Yemen, Syria and Europe working with Yemeni bombmakers. Eight of the 22 strikes in Syria targeted Khorasan, all west of Aleppo, U.S. military officials said.

There are likely several reasons for the overwhelming use of force in a single day. For one, Central Command officials said that the eight strikes against Khorasan were undertaken “to disrupt the imminent attack plotting against the United States and Western interests.” Additionally, because the U.S. military is not acting at the invitation of the government in Syria, any deployment of U.S. forces in the country’s airspace is more precarious than in Iraq — possibly making it more difficult for military commanders to plan repeated raids.

The State Department said Monday morning that the Obama administration had warned Syria that it “would not hesitate to take direction action” against Islamic State targets in Syria. But spokeswoman Jen Psaki said the administration did not request Syria’s permission or “give any indication of our timing on specific targets.”