As an integral part of modern infantry training specifically regarding the single file movement of troops, afoot or on patrol was an oft-heard admonition to
“Keep your interval!“
The interval or space between infantry soldiers on the move was to be rigorously maintained so as to prevent the felling of several soldiers with a single enemy gunshot, grenade, or worse, the loss of an entire group with a single burst of machine gun fire.
During the Việt Nam War
During in-country training in Việt Nam U.S. soldiers were instructed not to gather in groups of more than three when performing their regular duties or communicating with each other while “in plain sight of the enemy.” Furthermore, we were instructed not to look directly at each other while speaking, but to look over the other man’s shoulder so as to keep an eye out for muzzle flash in the treeline surrounding the base perimeter in the event of a sniper attack.
In light of the above, subdued (blackened) rank insignia became the standard issue and we were ordered not to salute superior officers; as they were the preferred target of snipers; as lower ranked personnel would normally salute their superiors and the officers were obliged to return the salute; thus identifying them from a great distance.
When too many soldiers were gathered together in a tight group (Again, “in plain sight of the enemy.”), a sergeant might be heard to say:
“Let’s break up this cluster fuck!”
A cluster fuck then is a non-sexual expression of U.S. military derivation first coined during the Việt Nam War era; descriptive of either a particular instance of the mass killing of troops or a gathering of soldiers that presents the potential for one.
“The 2017 Las Vegas massacre was the worst civilian cluster fuck in US history.”
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