The release of detainees from the United States prison at Guantanamo Bay has become a common enough occurrence this year that the process runs predictably and smoothly.

At the weekend it was the turn of six men who had been held for 12 years at the detention centre on the US Navy base in Cuba. They arrived in Uruguay as refugees on Sunday.

After a detainee is cleared for release, the US enters negotiations with a potential host nation.

When an agreement has been reached the detainee is informed and a representative of the International Committee of the Red Cross visits the detainee to ensure he is leaving voluntarily.

The detainee and representatives of the host nation meet for several interviews in preparation. The detainee might even receive language tuition.

About 24 hours before the detainee is due to leave, the centre's commanding officer will visit him to tell him he is about to be released. At present that role is held by Army Colonel David Heath.

"I've had some that are very unemotional, passive and others who have a big smile on their face when they are told they are leaving," Colonel Heath told Fairfax Media during a visit to Guantanamo Bay last week.

The detainees due to depart are then segregated from the rest of the centre's population until a flight arrives for them at the far end of the base called the Naval Air Station. Like everyone else who enters or leaves the base, known as Joint Task Force, the detainees leave for the airfield on a ferry.

The six men who made the trip this weekend - four Syrians, a Tunisian and a Palestinian – were held as suspected militants with ties to al-Qaeda, though they were never charged.

The release prompted criticism from Republican congresspeople who have successfully resisted President Barack Obama's attempts to close the facility.

"I've been opposed to the notion that we are going to farm out Gitmo to places," House intelligence committee chairman Mike Rogers said on Sunday during an interview on CNN's State of the Union.

"What we have found in the past is it doesn't work very well. I don't think that surprises anybody. So I argue that maybe we ought to rethink what we're doing here."

The men, named as Ahmed Adnan Ahjam, Ali Hussain Shaabaan, Omar Mahmoud Faraj, Abdul Bin Mohammed Abis Ourgy, Mohammed Tahanmatan and Jihad Diyab, were cleared for release as far back as 2010, but reports say the US struggled to find a country to accept them.

More recently outgoing US Defence secretary Chuck Hagel delayed the men's release. Then they were delayed by elections in Uruguay.

With the group's departure there remain 136 detainees in three facilities on the base.