I'm up, he sees me, I'm down.
This phrase is a training aid used by the United States Army during Basic Combat Training instruction of individual tactical movement.
The ideal exposure time for a soldier advancing position on the battlefield is 3-5 seconds. The theory being that it takes an enemy at least four seconds to aim a weapon at a moving target, and six to aim accurately. By repeating "I'm up, he sees me, I'm down." while moving towards a known enemy position, the individual soldier keeps within the limits of the 'safe' exposure time frame.
As the soldier prepares to move from behind cover, he first selects his next position within a desirable distance from himself.
At "I'm up," the soldier executes a combat roll to the left or right, gets to his feet and begins to rush forward.
At "he sees me," the soldier prepares to assume his next covered position.
At "I'm down." the soldier drops in place, situates himself behind adequate cover and begins to return fire.