Military operations depend heavily on communications and intelligence to be successful. When one or both of these elements becomes compromised, the result is often called the fog of war. The fog of war encompasses all of the confusions and miscalculations which can occur during an actual combat situation. There is also a political version of the fog of war, in which public opinion can be swayed by misinformation or ambiguous reporting of the facts.

One common event caused by the fog of war is called "friendly fire". Troops may be positioned on the battlefield according to a master plan, but those positions could change without warning during the actual battle. The results of this unplanned movement could be catastrophic, as friendly forces fail to recognize their comrades, or target positions thought to be clear of friendly troops. A number of accidental "friendly fire" deaths can be attributed to the fog of war.

Communication failures can also occur as a result of the fog of war. If the field commanders cannot relay vital course corrections or enemy positions to the operation center in real time, soldiers and military equipment could be put in harm's way. Such delays and miscommunications are typically blamed on the fog of war, since combatants may have to improvise a new strategy or retreat without sufficient time to relay their actions to headquarters. The fog of war can also work in the opposite direction, when vital orders from commanders cannot reach the battlefield in time.

The concept of a fog of war has come under considerable criticism over the years. Families of soldiers killed by "friendly fire" often blame their deaths on poor planning by superiors. The military's response to these allegations often includes an allusion to the fog of war, meaning that some battlefield casualties were due to real-time confusions or miscalculations, not poor planning. Some critics charge that the military depends too heavily on the fog of war defense to excuse their own actions or missteps.