The Army chief of staff said Thursday he's worried that a $6 billion combat communications system that has been under development for the past decade might not work, prompting frustration from senators.

Gen. Mark Milley told the Senate he will likely finish a "rigorous, thorough and painful" review in six weeks of the system, called the Warfighter Information Network-Tactical, to determine whether it can provide secure communications to soldiers in war zones as intended.

"The bottom line is, I have some serious hard questions that have not yet been satisfactorily answered as to whether it's going to work," Milley told the Senate Armed Services Committee.

The results of the review could mean the Army makes additional requests to Congress as lawmakers set their fiscal 2018 budget plans.

WIN-T is being developed to provide integrated wireless and wired communications between commanders and soldiers in the field and has included contracts with General Dynamics and Lockheed Martin.

Milley blamed the military's inefficient information technology acquisition process, saying it is too slow to keep up with changes.

"It's already been in development for 10 years," Milley said. "A lot of this stuff is already out of date."

Word that the long development may be failing after $6 billion in government investment riled Arizona Sen. John McCain, the Republican chairman of the committee, and some other members.

"Some of us feel frustrated," McCain said. "It's hard for us to continue to fight for more money [for the Army] when we see $6 billion wasted on one program."

Sen. Tom Cotton, a Republican Army veteran from Arkansas, said he had seen "credible reports" that WIN-T has ineffective line-of-sight communications, is too fragile to survive in war and has other serious problems.

The system "has an electromagnetic signature so loud that it practically would call for enemy artillery on the top of its users' heads," Cotton said.