What spotting would you make if you hear the impact of a round but are unable to visually acquire it after a CFF call?

In the scenario described, the appropriate spotting is "Unobserved." This term is used when a forward observer is unable to visually acquire the impact of the round following a call for fire. It indicates that while the observer is aware that a round has impacted (as evidenced by hearing the sound), there is no visual confirmation of the round's effects on the target.

Using "Unobserved" in this situation communicates to the fire support team that the observer cannot see the outcome of the round, which is crucial for subsequent adjustments. This allows for an effective response to ensure accurate targeting in further engagements.

The other options do not accurately represent the situation. "Doubtful" implies uncertainty about the effectiveness or accuracy of the fire, which would require further clarification and could lead to miscommunication. "Lost" generally refers to a situation where the observer has lost contact with the target or control of the mission, indicating a higher level of confusion. "Cannot Observe" suggests an inability to see the impact altogether, but it lacks the specificity needed in the call for fire context. Thus, "Unobserved" is the most precise term to use in the given scenario.