If target length, or length and width are given, the observer must also give what additional detail?

The correct answer is that the observer must also provide the attitude. In military terms, particularly when dealing with artillery and target acquisition, "attitude" refers to the target's position in relation to the observer’s viewpoint, which can include the target's orientation or any vertical positioning changes. It's crucial for effective target engagement to understand not just the dimensions of the target but also how it is positioned in the field of fire.

While depth, radius, and altitude might seem relevant, they do not capture the necessary details about how the target is positioned or perceived. Depth typically refers to the distance from the front of the target to its rear, which, although relevant, does not encompass orientation. Radius may pertain to circular or spherical targets but does not apply broadly to all target shapes. Altitude refers to the height of the target above a given reference point, which is important but secondary to understanding the target's attitude at the time of observation. Thus, emphasizing the attitude provides critical context for proper targeting and engagement planning.