Hart's War

During World War II, U.S. Army intelligence officer First Lieutenant Thomas Hart (Farrell) is captured by German forces. While interrogating Hart, the Germans coerce him to divulge intelligence by taking away his boots, causing his feet to become frostbitten and badly injured, and leaving him, naked, in a very cold cell. He is then transferred by train to Stalag VI-A prisoner of war camp at Hemer, Germany. While en route, a P-51 Mustang attacks (the letters POW were painted on the top of the train, but got covered by thick snow). To save themselves, the POWs leave the train and spell P-O-W with their bodies and prevent further strafing.
After arriving at the new POW camp, Lt. Hart is interviewed by the ranking American officer, Colonel William McNamara (Willis). When McNamara asks if he cooperated with the Germans after he was captured, Hart denies it. McNamara knows this to be a lie when Hart says he only endured three days of interrogation. McNamara does not reveal this to Hart, but sends him to bunk in a barracks for enlisted men, rather than allow him to bunk with the other officers.
Two black pilots are brought to the camp and assigned to Hart's barracks. They are the only blacks in the camp, and their situation is compounded by their status as officers. Staff Sgt. Vic W. Bedford (Hauser), a racist, is their primary antagonist. One of the pilots, Lt. Lamar Archer, is executed when accused of keeping a weapon that Bedford had planted in his bunk. When Bedford himself subsequently turns up dead, the surviving pilot, Lt. Lincoln A. Scott (Howard) is accused of killing Bedford in retaliation. A law student before the war, Hart is appointed by McNamara to defend the accused pilot at his court-martial, a trial to which the camp commandant, Oberst Werner Visser (IureÅ) agrees.
Much later, McNamara reveals to Hart that the "defense," like the trial itself, is a sham, an elaborate distraction to hide a planned attack on a nearby ammunition plant (the U.S. Army mistakenly believes it to be a shoe factory) by McNamara and his men, in aid of the war effort. It is revealed that Bedford planted the weapon in Archer's bunk, knowing the guards would kill him for it. In return, he gave them the location of a secret radio. It is also revealed he planned to escape with money and clothes, likely in return for telling the Nazis about McNamara's plan. McNamara realized this, and killed Bedford to prevent it. Hart is shocked that McNamara as a senior officer would sacrifice a fellow American (Scott) to protect the planned attack on the ammunition plant. McNamara reminds Hart that in war, sometimes one man must be sacrificed to save the lives of many. Hart acknowledges this, but retorts that it is McNamara's duty to ensure that he (McNamara), not Lincoln Scott, is the sacrifice. Disgusted, McNamara says that Hart does not know anything about duty, in reference to how Hart gave into a "Level 1" interrogator after three days, whereas McNamara was tortured for a month.
McNamara's ploy nearly succeeds. The escaped soldiers destroy the nearby ammunition plant. However, at the end of the court-martial, Hart falsely confesses to Bedford's murder in order to save Lt. Scott. McNamara overhears Hart's confession; McNamara has a change of heart and voluntarily returns to the camp to accept responsibility. Visser holds McNamara accountable and personally executes him on the spot, but spares the remaining prisoners. Three months later, the German army surrenders to the Allies. The prison camp is liberated and all of the surviving prisoners, including Hart, are sent home. Hart's final comments are that he learned about honor, duty and sacrifice.

Question: What was painted on the top of the train?
Answer: POW