There was a sci-fi story decades ago (probably in Analog) on this theme. A very realistic war game was set up, which two real-world opposing nations decided to

There was a sci-fi story decades ago (probably in Analog) on this theme. A very realistic war game was set up, which two real-world opposing nations decided to use in lieu of losing real men. The friction caught them off guard. The one incident I recall was when one side deployed a biowarfare agent, but the wind changed and they ended up infecting their own troops. There were other incidents of friction.