A new government watchdog inquiry shows the difficulty in retaining Afghan fighting forces — and even in finding the ones already on the payroll.

Since 2002, Congress has appropriated more than $68 billion for Afghan national defense, including funding for the Afghan National Army and the National Police. But persistent reports indicate discrepancies between the assigned number of forces and the actual number who are serving.

The phenomenon has a name: "ghost soldiers."

The Office of Special Inspector General for Afghanistan Reconstruction last week released a letter it sent to Secretary of Defense Ashton Carter seeking answers about what the Pentagon is doing to make sure it is paying for security forces that actually exist.

As much as $300 million in annual U.S. salary payments to the Afghan National Police may be based on partly verified or unreconciled data.

In July, the U.S. military reported Afghan defense strength at 319,595. But the Associated Press quoted a high-level Afghan official as saying the best internal estimate was around 120,000.

More recently, Afghan government officials have raised concerns about ghost soldiers and police in Helmand Province. The new police chief of Helmand was quoted as stating that as many as 40 to 50 percent of the approximately 26,000 personnel assigned to the province did not exist when he asked for help during operations. Much of the money appeared to be going into someone's bank account.

Among other things, the inspector general is asking the Pentagon to provide an update on efforts to use electronic tracking and biometric systems to identify and eliminate the problem of ghost soldiers and police.

The problem has been going on for years.

Back in 2009, former Star Tribune photographer Rick Sennott and I visited an Afghan Army base near Mazar-i-Sharif in northern Afghanistan, where we witnessed the dysfunction of the Afghan military and American attempts to reform it. A small group from the Minnesota National Guard had been assigned to assist in training.

Row after row of new dump trucks, front-end loaders, Ford Rangers and Humvees sat in neat formation at the base, plastic wrapping still on the seats, shipping tags still pasted on the windows. They'd been idle since arriving a year earlier because the Afghans didn't know how to operate them.

Many of the Afghan officers and older soldiers were veterans of the war with the Soviets in the 1980s. Some were members of the mujahedeen — the jihadist guerrillas who rebelled against the Soviets — while others served with the government army that fought alongside them.

Ethnic and religious divides split the army. Corruption was rampant in some areas, with supplies stolen for resale. Soldier pay was being increased, but the Afghan "cash men" assigned to handle payrolls pocketed some of the cash or charged fees to hand out pay.

Even when the pay did come through without a problem, it paled against what the Taliban was offering for service on the other side of the firefights. During harvest season, many soldiers simply went home and never returned.

Military commanders don't normally set humble goals, but the expectations were unusually modest.

"When you start out, you usually ask yourself how many touchdowns are we going to score before we go home," the commander of the Guard unit said at the time. "With this assignment, we're hoping to move the ball ahead maybe five yards when we're done."