When two units are specified in the message to observer, what does this indicate about the mission?

When two units are specified in the message to observer, it indicates an "Adjust Fire" mission. In this context, "Adjust Fire" refers to sending a message that includes both the target location and the initial data necessary for the observer to make corrections based on observed effects. The presence of two units allows the observers to receive feedback and make necessary adjustments to the fire mission to accurately engage the target.

The "Fire for Effect" option typically refers to a situation where no adjustments are needed, and the artillery units are instructed to fire with full effect on the target after initial corrections have been made. Suppression fire emphasizes momentarily disrupting an enemy force's actions, but it doesn't indicate the need for two units for adjustment. "Deliver Fire" is not a recognized term in the call for fire process and does not apply in this scenario.

Thus, indicating that two units are involved aligns specifically with the procedure of adjusting fire based on initial targeting information, making this option the correct choice.