Robert Gates said Friday that the U.S. military is unprepared for the 'evolving internal security threat.' (J. Scott Applewhite/Associated Press)

A Pentagon investigation has found that military bases in the United States are not sufficiently prepared to prevent attacks similar to the Fort Hood massacre last year, Defence Secretary Robert Gates said Friday.

Commanders must be encouraged to intervene if they believe someone within the ranks is a potential threat, Gates said during a news conference. He asked Army Secretary John McHugh to make changes and said he expects new policies to be in place by summer.

Gates made his remarks ahead of the release of the investigation report Friday. The document stated the U.S. military "did not have a comprehensive training program focused on internal threats regardless of the target."

The internal review of the events that took place at the Ford Hood military base in Texas on Nov. 5 revealed that supervisors had repeatedly complained about the erratic behaviour and religious zealotry of the soldier accused of carrying out the shooting rampage, Maj. Nidal Hasan.

A military psychiatrist at Fort Hood, Hasan is charged with killing 13 people and injuring 43 in one of the deadliest mass shootings to ever take place at an American military base.

Despite the documented concerns about Hasan, he was regularly praised in performance reviews and promoted through the ranks.

The report said that a number of medical officials failed to show "appropriate judgment and standards of officership" when conducting performance reviews of the alleged shooter.

Two officials familiar with the case, speaking on condition of anonymity, said the U.S. military may reprimand up to eight officers in relation to the incident.

Among the review's findings is that Hasan's top-level security clearance was not properly investigated. Had policies been followed properly, investigators say his clearance might have been revoked "and his continued service and pending deployment would have been subject to increased scrutiny."

Review recommends more training, guidelines

Gates, who ordered the investigation two weeks after the shooting, declined to discuss disciplinary action or specifics of the review. He did say the findings showed that "it is clear that as a department we have not done enough to adapt to the evolving internal security threat."

Gates also said it demonstrates that the Pentagon "is burdened by 20th century processes and attitudes mostly rooted in the Cold War."

The report included several recommendations for the U.S. military to help prevent another incident like the Fort Hood shooting.

One key suggestion is for the military to develop programs to train base officers to recognize suspicious behaviour among fellow troops and colleagues. The review noted that several organizations, including the navy and the U.S. Postal Service, already have similar programs in place.

Another recommendation is to provide base supervisors with clear guidelines regarding religious accommodation to help them distinguish between appropriate religious practice and behaviour that "may indicate a potential for violence or self-radicalization."