The US Air Force came under fire after admitting it failed to submit the gunman Devin Patrick Kelley's name to the FBI's background check system

More than 4,000 names have been added to the country's list of ex-military members banned from owning firearms since the Sutherland Springs massacre last November, a CNN report has found.

In the aftermath of the tragedy, the US Air Force came under fire after admitting it failed to submit the gunman's name to the FBI's background check system - even though he had been kicked out of the military for assaulting his wife, which should have prevented him from owning a firearm under federal law.

Still, the ex-airman was able to purchase a semiautomatic rifle that he used to kill 26 people and injure 20 others at the First Baptist Church church in Texas, exposing a massive hole in the nation's background check system.

Since then, 4,284 names have been added to the FBI's list of dishonorably discharged military personnel banned from owning firearms - an increase of 38 per cent.

It is the law that anyone who receives a dishonorable or misconduct discharge should automatically get banned from owning a firearm.

The FBI's list of banned servicemen and women hovered at about 11,000 since 2015, but that number jumped to 14,825 in November and then to 15,583 in December.

Now, the number stands at 15,597, the review of FBI statistics found.

The ex-airman was able to purchase a semiautomatic rifle that he used to kill 26 people and injure 20 others at the First Baptist Church church in Texas (pictured)

As CNN points out, more than 4,000 unfit people could have bought weapons while they were kept out of the FBI's list of dishonorably discharged ex-service members.

The Department of Defense has not yet acknowledged the military has highly expanded the list since the tragic shooting.

But the the US Marine Corps, Air Force and Navy admitted that they have been going through old records.

'We are in the process of conducting a thorough review of past cases to ensure that any prior failures to report are rectified and the appropriate information is provided to the FBI,' Capt. Christopher R. Harrison, a spokesman for the Marines, told CNN.

The US Army declined to comment, citing a pending lawsuit about its failures to report these types of cases. The US Coast Guard, on its part, said it always reports to the FBI on time, so its numbers aren't part of the recent spike.

The Department of Defense has not acknowledged the military has highly expanded their list of dishonorably discharged members since the tragic shooting (stock photo of the Pentagon)

Rep Scott Taylor, of Virginia, told CNN: 'I'm encouraged that they're trying to hurry up and get through this backlog. But it was a failure of duty and responsibility to not report these people to the federal database. I'm highly disappointed.'

A dishonorable discharge happens when members are convicted by the military of violence or serious, felony-level crimes, while a bad-conduct discharge happens with drug-dealing and domestic violence offenses, such as the Texas gunman's.

Although the Texas shooter received a bad-conduct discharge, only cases of dishonorable discharges are reflected in the recent spike.

The armed forces are required to report dishonorable and bad-conduct discharges to the FBI, as both ban people from owning firearms, but they have long struggled with reporting all of these cases.

In 1997, a general inspector report found the Navy failed to notify the FBI of dishonorable and misconduct discharges 93 per cent of the time, and the Army 79 per cent of the time.

The Pentagon's Office of Inspector General is currently investigating how the Air Force failed to report Texas shooter Devin Patrick Kelley to the FBI.