The raid, according to multiple military and intelligence officials and a post-battle briefing paper shared with NBC News, had been planned and prepared for months, and was part of a long multinational campaign to weaken the foothold of al Qaeda in the Arabian Peninsula (AQAP), long considered one of the most dangerous arms of the terrorist organization.
AQAP has a history of attacks against the U.S. and its allies, including the Christmas Day 2009 attempted bombing of a commercial airliner in the United States, the failed parcel bomb plot of 2010 and the January 2015 Charlie Hebdo office attack in Paris.
The U.S. has been trying to dismantle AQAP since 2002. In addition to drone and air strikes — there were a half dozen drone strikes in 2016 — the U.S. has also used boots on the ground. Small numbers of U.S. military personnel have engaged in unilateral operations against AQAP leaders and in support of Yemeni and coalition special operations forces.
The U.S. began preparations for Sunday's raid on the al Qaeda camp months ago, according to a senior military official. The intent of the "site exploitation" mission was to capture important information about a terror network's personnel and supplies from a specific house in the al Qaeda camp near Ghabat Yakla in south Yemen.
Planning was intense, with almost three months of intelligence collection — including "pattern of life" constant surveillance of the target home and the families in nearby dwellings.
Because the targeted house was particularly well guarded, officials say, the "package size," or the volume of troops and materiel needed, was larger than usual.
In early December, the USS Makin Island and its amphibious readiness group, including other ships and Marines, arrived in the area to serve as the quick reaction force for American operations in Yemen. They were joined in Djibouti by the Navy SEALs who would make up the main raiding party.
On Dec. 21, the SEALs joined the Marines in a helicopter-borne training raid in Djibouti, an exercise that served as a rehearsal for Sunday's mission.
The Obama administration then had to decide whether to carry out the mission.
A former senior Obama administration official said that plans for the raid were presented to the Obama national security team before the inauguration as part of a menu of potential actions that represented a significant expansion of U.S. activity in Yemen. After a full interagency review, the official said, the Obama administration decided to pass the decision on the series of operations off to the Trump administration, since they would have to commence under the new president.
The hesitation, the official said, related to the number of troops that would be involved and that the plans represented a wider use of ground troops than the U.S. had previously considered in Yemen. The official said the specific raid mounted on Sunday was not presented for a decision.
White House spokesman Sean Spicer said Wednesday that the raid was approved in an interagency deputies meeting on Jan. 6, and that the plan called for the raid to take place on a moonless night, which meant it would occur after Trump's inauguration.
The former Obama official, however, said the interagency deputies committee of the National Security Council did not officially recommend for or against the raid.
Ned Price, a former CIA officer who was spokesman for the National Security Council during the Obama administration, said in a tweet that Spicer was wrong and that the "specific operation in question was never presented to or considered by the Obama Admin for approval."
According to a former special operations officer with knowledge of the raid, one of the Obama administration's concerns was the integration of commandos from the United Arab Emirates, an unusual arrangement for the Joint Special Operations Command (JSOC) and its elite task forces. In some ways, said the retired officer, it was an Emirati-driven operation, with their intelligence on the ground and their year-long preparation.