The British Army is using a specially developed version of the celebrated computer game Half-Life to train its troops.
With the first-person shoot-em-up soldiers can try out new weapons and new tactics without encountering real bullets and bombs.
The Ministry of Defence hopes the system may help reinforce some of the lessons learned on more traditional training exercises.
Like the popular modification, or mod, of Half-Life known as Counterstrike, the army version allows up to eight soldiers to go into virtual combat at any one time.
The troops work as a unit, moving about a simulated environment to track down and confront an enemy.
Similarly, a typical Counterstrike game pits two teams of four players against each other, with one side playing terrorists and the others the counter-insurgent troops.
Using a mouse and keyboard, the soldiers can fire their guns, throw grenades and even plant plastic explosives.
"It"s clear to us - particularly me as a military observer - that these guys are really engaged in what they are doing; it is not just a game played across a keyboard and a mouse. They want to succeed just as they want to in real training."