The U.S. Army's $5 billion intelligence network, which is designed to give commanders battlefield awareness but has been criticized for years as a boondoggle, was not working in Afghanistan during the recent American air attack on a hospital, according to a member of Congress who has been in touch with military whistleblowers.

Significant elements of the Distributed Common Ground System, a network of computers and sensors designed to knit together disparate strands of intelligence, were off line in Afghanistan when U.S. commanders approved an air strike Oct. 3 that killed 22 staff, patients and others at a Doctors without Borders hospital in Kunduz, Rep. Duncan Hunter wrote Tuesday to Defense Secretary Ash Carter.

"The purpose of DCGS is to enable commanders and service members to 'see and know' the battlefield and prevent incidents like the airstrike on the hospital in Kunduz," wrote Hunter, a California Republican, combat veteran and armed services committee member who has been a persistent DCGS critic.

"Senior Army leaders have gone to extraordinary lengths in recent years to deny evidence of the failures of the DCGS program, and I am asking for your help to prevent them from doing so following this tragic incident," he wrote.

Pentagon spokesman Peter Cook did not immediately respond to a request for comment.

It's unclear whether the breakdown of key DCGS systems contributed to the decision to approve the air attack, which Pentagon officials say was a mistake. But the coordinates of the hospital were entered into an intelligence database that is part of the DCGS intelligence network, according to a U.S. official who would not be quoted because he was not authorized to discuss the matter.

The Army over the years has touted DCGS as having "saved lives" with its ability to fuse together various intelligence sources, including drone footage, mapping software, human source reports, social media and eavesdropping transcripts. But independent Army testers repeatedly have questioned the system's effectiveness. One testing report in 2012 said it was "not survivable," meaning it was at risk of failing in combat.

The Associated Press has reported that special operations intelligence analysts knew the Doctors without Borders facility was a hospital, and were circulating intelligence reports about possible enemy activity at the site. Some of those analysts were using a commercial software system made by Palantir, a Silicon Valley company that competes with DCGS, according to an Army official who would not be quoted because he was not authorized to speak publicly.

President Barack Obama apologized for the air attack to Dr. Joanne Liu, the international president of Doctors without Borders, who has called for an independent international investigation. U.S., NATO and Afghan investigations are looking into the matter. The U.S. has offered to compensate the families of those killed and injured.

Pentagon officials have said the military did not intentionally target the hospital, but they have not explained why the Army analysts who knew it was a medical facility were not able to convey that intelligence to commanders who approved the air strike.

Among the elements of DCGS that were not working, service members told Hunter, were the intelligence fusion server, which is supposed to allow seamless information sharing across various Army elements, and the cloud, which is supposed to offer connectivity to units in the field.

Hunter told Carter that his sources say they fear for their careers if they speak out publicly, because "members of Army leadership have previously gone to great lengths to protect this system and its proponents."

"Army Brigade commanders have told me of intimidation and threats after saying in writing that DCGS 'translates into operational opportunities missed and lives lost,' Hunter wrote to Carter. "Such actions are indicative of a climate that is contradictory to a transparent and objective assessment of the facts with respect to this system."

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