Behind Enemy Lines

In the final stages of the Bosnian War in December 1995, United States Navy flight officer Lieutenant Chris Burnett and pilot Lieutenant Jeremy Stackhouse, who are stationed on the aircraft carrier USS Carl Vinson in the Adriatic Sea, are assigned a reconnaissance mission by their commanding officer, Admiral Reigart. The mission goes smoothly until they spot suspicious activity in the demilitarized zone where NATO aircraft and the warring factions are prohibited from engaging in military activity. Burnett persuades Stackhouse to fly their F/A-18 Hornet off-course to get a close look and photograph the target. They are unaware that they photographed mass graves, and Serb soldiers see the jet. The local Bosnian Serb paramilitary commander, General Miroslav Lokar, is conducting a secret genocidal campaign against the local Bosniak population. Not wanting the mass graves to be discovered, Lokar orders the jet be shot down.
Despite trying to outmaneuver the missiles fired at them, their jet is hit and both men are forced to eject. Shortly after touching ground, a Serb patrol finds an injured Stackhouse and interrogate him. Stackhouse is then executed by Sasha, one of Lokar's right-hand men. Burnett, who was observing the Serbs' interrogation of Stackhouse from a hill, flees the area, but exposes his location. Wanting Burnett dead as well, Lokar orders both his deputy, Colonel Bazda, and Sasha to find him. After Burnett contacts Admiral Reigart for help, he orders Burnett to move to a certain location in order to be extracted. However, Reigart is forced to stand down after Admiral Piquet, the commander of NATO naval forces in the region, warns him that rescuing Burnett in the demilitarized zone risks derailing the peace process. When Burnett reaches the extraction point, Reigart informs him that he must move to another location miles outside of the demilitarized zone in order to be rescued.
Immediately after being informed, Burnett sees a Serb patrol, led by Bazda, looking for him. Running from them, he falls into the mass grave that he and Stackhouse had photographed and hides under a dead body. When the patrol is out of sight, he continues to run. On his way to the new extraction point, Burnett encounters a group of Bosniak guerrillas in a pickup truck who offer him a ride. The guerrillas inform Burnett that they are heading to HaÄ, which is supposedly a safe haven but turns out to be a war zone. During the battle, Serb troops believe that they have found Burnett's body, but Sasha realizes that Burnett had switched uniforms with a dead Serb soldier and escaped HaÄ.
The Serbs turn the situation to their advantage, presenting the corpse wearing Burnett's uniform to the media, and saying he was killed by guerrillas. The ruse works and a mission to rescue Burnett is aborted. However, Burnett notices an angel statue near where his ejection seat landed. He returns to his seat and activates the rescue beacon. Though the carrier group notices his signal and positively identifies him, Burnett has also alerted the Serbs to his location.
Knowing he risks being relieved of command, Reigart prepares a task force to rescue Burnett in open defiance of Piquet's orders. Meanwhile, Bazda and Sasha are ordered by Lokar to find Burnett and kill him, but on their way, Bazda steps on a landmine and Sasha abandons him to his fate. The mine eventually explodes, alerting Burnett that someone is following him. After Sasha finds the ejection seat, Burnett ambushes him and the two men engage in hand-to-hand combat until Burnett stabs Sasha. Immediately after Sasha is killed, Lokar arrives with armored vehicles and infantry who open fire on Burnett. After retrieving the hard drive containing the photos of the mass graves, Burnett escapes with the task force.
The conclusion reveals that the footage Burnett retrieved leads to the arrest and conviction of Lokar for war crimes including genocide, while Reigart's actions result in him being relieved of command and his eventual retirement. Burnett continues his career in the Navy.

Question: What does Sasha realize Burnett has switched with a dead soldier in order to escape Hac?
Answer: Uniforms