By the end of the year, NATO will have spent $20 billion on developing Afghan security forces since the start of 2010 and will maintain a training presence through at least 2016, the commander of the training mission said Wednesday.

Soaring illiteracy rates among service members and a shortage of specialized trainers, however, remain major hurdles as Afghans prepare to take control of securing their nation by the 2014 deadline for NATO to withdraw combat forces, said U.S. Lt. Gen. William Caldwell.

"We have made great strides in providing the Afghan national security force with both capable and sustainable weapons, vehicles and equipment over this last year, while building a very strong and self-reliant security force," Caldwell said.

The $20 billion for 2010 and 2011 is paying for training, equipment and infrastructure. The figure is a large increase over the $20 billion spent between 2003 and 2009.

"We're already seeing the results," Caldwell said.

Those include the growth of the Afghan army, police and air force by about 70,000 people over the past 12 months. New vehicles and aircraft have been ordered, as have an array of weapons ranging from machine guns to mortars, uniforms, night vision goggles and other equipment.

The mission still needs 397 specialized trainers such as doctors, nurses, logisticians and maintenance specialists, Caldwell said.

Nonetheless, progress has been made.

The Afghan army now has 149,553 personnel, according to NATO figures, and is projected to grow to 171,600 by October. The air force is slated to grow from 4,098 personnel in December to 5,500 by November. The police force, meanwhile, is projected to hit 134,000 by October, up from 115,584 by the end of last year.

Caldwell said the NATO training mission would remain as long as necessary, but at least until 2016, when it expects to finish developing the air force.

"We're not leaving," he said. "If anything, our organization will probably grow a little bit more in size."

Among remaining challenges are illiteracy rates as high as almost 85 percent for enlisted service members and only slightly better for noncommissioned officers, NATO commanders say.

"It's a matter of life and death," Caldwell said. "If they can't read a number and a letter, they can't read a map. If they can't read a map, they can't call in artillery fire, helicopter support, aircraft support."

Developing the air force is another challenge.

Training pilots is a roughly two-year process, and NATO has so far focused on meeting the military's present needs of battling the insurgency.