Final answer:
The observer needs to provide the target description, length, width, and orientation of a linear irregularly shaped target in the third transmission of the call for fire.
Step-by-step explanation:
In the third transmission of the call for fire, the observer is required to send the target description, length, width, and orientation of a linear irregularly shaped target. The orientation refers to the direction or angle at which the target is set. It is important for the observer to communicate this information accurately to ensure effective fire support.