Animal-rights activists are calling on the U.S. to stop using animals as subjects to help train its military, calling the medical and trauma exercises cruel and a disservice to the troops.

The People for the Ethical Treatment of Animals sent a letter today to Defense Secretary Robert Gates asking him to replace the use of animals with non-animal methods such as human simulators.

In the letter, PETA said the military inflicts gunshot, burn and chemical wounds on monkeys, pigs and goats for training.

"This outmoded practice is not only cruel, but is a disservice to the men and women who risk their lives in defense of our country and who deserve the most effective trauma training methods available," wrote Kathy Guillermo, director of the PETA's Laboratory Investigations Department.

The Pentagon did not immediately return calls seeking comment.

PETA's letter comes 10 days after the group failed to prevent the Army from shooting live pigs and treating their gunshot wounds in a medical trauma exercise at Schofield Barracks.

The soldiers were with the 3rd Infantry Brigade Combat Team, 25th Infantry Division, which is deploying to Iraq this year.

The Army said the training is critical to teach soldiers how to manage critically injured patients within the first few hours of their injuries when there are no medics, doctors or facilities nearby.

PETA believes the military's Combat Trauma Patient Simulation system, which is being used at other bases such as Camp Pendleton in California and Camp Lejeune in North Carolina, is a more advanced and humane option.

In its letter, the Norfolk, Va.-based group cited a 2006 New York Times report that quoted a Navy medic who described the training he witnessed involving pigs.

"They shot him twice in the face with a 9-millimeter pistol, and then six times with an AK-47 and then twice with a 12-gauge shotgun. And then he was set on fire. ... I kept him alive for 15 hours. That was my pig."

PETA also noted the Department of Defense's animal welfare policy that states, "Alternative methods to the use of animals must be considered and used if such alternatives produce scientifically valid or equivalent results to attain the research, education, training, and testing objectives."