[siempre_fidelis]

I thought it was Andrew Jackson at the battle of New Orleans who told his men not to fire until they saw the whites of their eyes.

[Tallguy]

The quote comes from Bunker Hill. But it was good tactical advice in the era of the smoothbore musket (which included the Battle of New Orleans in 1815). You couldn’t reliably hit anything beyond 50 yards — roughly the distance at which you could discern the “whites of the eyes” of the advancing enemy infantry.