NATO Secretary General Rasmussen addresses a news conference on Libya at the Alliance headquarters in Brussels, March 24, (Reuters).
The codename for NATO's operations in Libya, "Unified Protector", hides internal divisions that the alliance battled hard to overcome before taking on the mission.
The 28-nation military organisation is finally fulfilling Washington's wishes, replacing the United States at the helm of all operations in Libya and is expected to be fully up and running by Thursday.
But to get to this point, the alliance had to ease Turkish concerns about the scope of the bombing campaign against Muammar Gaddafi's forces and convince France that NATO should be in command of operations.
Germany was opposed to any military intervention from the outset, refusing to vote for the UN Security Council resolution that authorised "all necessary measures" to protect Libyan civilians.
Despite the squabbles, NATO is enforcing an arms embargo and a no-fly zone, and it finally agreed on Sunday to take over the riskiest mission: preventingGaddafi loyalists from massacring the population.
Most NATO members, most prominently Britain and Italy, wanted the alliance to take charge of the US-led campaign that began on March 19, but not all alliance members will participate in the bombing missions.
Even though they are long-standing members of NATO, Turkey and Germany will not take part in air strikes on ground forces, although Ankara has offered warships and a submarine to enforce an arms embargo.
Turkey, NATO's only Muslim member, is a major player in the region and was loath to take part in any mission that involved risky ground strikes.
"There has always been this division within the alliance about projecting power in the global war on terror," said Ian Davis, director of the NATO Watch think tank.
"That is reflected in the make-up of countries providing forces" in the Libya campaign, he said.
France wanted to keep political control of the bombing operations in the hands of an international coalition, arguing that NATO had a bad reputation in Arab countries that the allies want to bring into the mission.
It took a week of marathon talks for NATO ambassadors to agree on the mission. They also endorsed rules of engagement drafted by alliance military planners limiting air strikes to the prevention of civilian casualties.
French and German envoys briefly walked out at one session over criticism from NATO Secretary General Anders Fogh Rasmussen, while Italy's foreign ministry lashed out at Paris for being "intransigent" about giving NATO the lead.
The alliance now faces an uncertain endgame in Libya, with Western military officials warning the conflict could last weeks or even months.
Although NATO adopted a 90-day military plan, alliance officials say the mission is renewable and will only end once the United Nations decides it must stop.
Allies have sent mixed signals about their goals.
US President Barack Obama says the aim of the mission is not to oust Gaddafi by force, although he said Tuesday that he was confident the Libyan leader would "ultimately step down."
France said it was prepared to hold discussions with allies over whether to arm the rebels, an option the Obama administration has not ruled out.
But Rasmussen told CNN that the mission's aim is to shield civilians, not arm the rebellion.
"The UN mandate authorises the enforcement of an arms embargo," Rasmussen told the US news network on Monday. "We are not in Libya to arm people, but to protect people."