When should the alternate method of direct fire be used?

The alternate method of direct fire should be used when the M90A3 is out of boresight or unserviceable because this situation directly affects the ability of a cannon crew to accurately aim and fire the howitzer effectively. The M90A3 is a critical component for ensuring precision in targeting; if it is not functioning correctly or cannot be properly aligned, the crew must rely on an alternative method to achieve effective direct fire capabilities. This ensures mission continuity and the safety of personnel by allowing for accurate engagement despite equipment issues. Understanding this reliance on the M90A3 underscores the importance of maintaining operational readiness for primary targeting systems.