What is the HOB correction when one airburst and three graze bursts are spotted?

The correct answer is determined by understanding the concept of height of burst (HOB) corrections in artillery and air support. When analyzing different types of bursts from munitions, an airburst occurs when a round detonates above the target, whereas graze bursts happen when rounds impact just above ground level, nearly grazing the surface.

In the scenario presented, there is one airburst, which signifies a potential deficiency in the elevation of fire compared to the intended target. The presence of three graze bursts suggests that the rounds are not impacting effectively on target, potentially indicating that the elevation is again too low.

To address both types of bursts, an HOB correction is needed. The standard corrective measures for these situations typically are cumulative – with airbursts commonly calling for a more significant adjustment. When an airburst is present along with multiple graze bursts, the total correction required is determined by adding the necessary corrections for both the airburst and the graze bursts.

In this case, the necessary correction leads to an "Up 20" for the airburst, alongside an additional increment for the graze bursts, which altogether totals "Up 40". Thus, this reasoning aligns with the answer indicating that the proper correction in this scenario would indeed be