Other public health officers, who worked at Guantánamo in the past year, described conditions there for the detainees, some of whom first learned they were in Cuba from the nurses and doctors sent to care for them. They treated immigrants detained in a dark prison called Camp 6, where no sunlight filters in, said the officers who have been granted anonymity because they fear retaliation for speaking publicly. It previously held people with suspected ties to Al Qaeda. The officers said they were not briefed ahead of time on the details of their potential duties at the base.