Defense Department officials said around 1,200 Syrian opposition fighters were identified as potential candidates for the training; according to recent reports, 400 have passed the initial security screening, and will soon begin the training, subject to final approval.
The first of the 400-strong cohort of military trainers have recently arrived in Turkey and Jordan in preparation for carrying out the training, which aims to train more than 5,000 rebels annually for three years, covering small arms, radio communication, battlefield tactics and medical equipment. The rebels will also be provided with weapons, trucks and tactical radios.
The number of trained rebels is also far outnumbered by the Islamic State's fighting force, which is estimated by the CIA to have more than 30,000 fighters.
The current mission is an escalation of a covert CIA-led program to train Syrian fighters which began in Jordan in 2013, and is also an expansion of the US policy in Iraq, where more than 3,000 troops have been sent to train Iraqi and Kurdish forces.
On December 4, the US House of Representatives extended the president's authority to train and equip moderate Syrian rebels by two years as part of the $585 billion annual defense authorization bill, which also authorized $6.6 billion for operations against the Islamic State.