What must unit drivers do before leaving the ASP with ammunition?

Using DA Form 3151 to take inventory is essential for unit drivers before they leave the ASP (Ammunition Supply Point) with ammunition because this form is specifically designed to document the inventory of ammunition. It ensures that a detailed record is kept, which includes quantities, types of ammunition, and any discrepancies that might affect accountability.

Accurate completion of DA Form 3151 helps maintain a chain of custody and allows for proper tracking of ammunition as it is issued and turns in. This procedure is crucial in military operations for ensuring that the right types and amounts of ammunition are in the hands of authorized personnel, thus supporting operational effectiveness and safety protocols.

The other options, while related to the process of handling ammunition, do not specifically focus on the critical requirement of inventory documentation immediately before departure from the ASP. This makes using DA Form 3151 the correct procedure for unit drivers.