How many times does Fred Allison try to escape captivity?

British Captain Fred Allison bids farewell to his new wife, Monica, whom he has only known for six days, and sets out to serve in World War I. He ends up a prisoner of war (POW), tortured by the fact that his wife has not written to him since the early days of his two year captivity.

When a fellow inmate shoots a guard, the prisoners make an impromptu unsuccessful dash for freedom, resulting in much bloodshed on both sides. As punishment, they are locked in a crowded cell for about a month. Finally, a new commandant, Oberst Carl Ehrlich, takes charge of the camp. Allison persuades Ehrlich (a fellow Oxford alumnus) to rescind the punishment.

One day, a fresh batch of POWs arrives. Allison is delighted to find his oldest and best friend among them, Royal Flying Corps Lieutenant Jack "Dig" Digby. For some reason though, Dig is not as pleased to see him. However, Allison attributes that to their situation. Dig is determined to escape, regardless of the consequences to his fellow prisoners. He does manage to break free, stealing an aircraft from the nearby airfield.

It seems from the text that Fred Allison tried to escape one time.

The prisoners made an impromptu unsuccessful dash for freedom when a fellow inmate shot a guard. We don't know for sure, but we can assume that Fred Allison was one of the prisoners that attempted to escape. Dig, Allison's oldest and best friend, managed to break free by stealing an aircraft from a nearby airfield, but it does not appear that Allison was involved.