Which of the following is part of the pre-fire safety checks for a 60mm mortar?

The pre-fire safety checks for a 60mm mortar are critical to ensure safe operation and effective engagement. One key aspect of these checks is ensuring that the selector switch is set correctly. The correct positioning of the selector switch to "drop-fire" indicates that the mortar is prepared to fire safely when subjected to the proper firing conditions. The "drop-fire" setting minimizes the risk of an unintended discharge, allowing the mortar to fire only when the round is properly placed in the tube and the mortar is ready to engage the target.

While the other considerations play a role in overall mortar operation, they are not pertinent to the pre-fire safety checks. For instance, disassembling the cannon or disconnecting the bipod would indicate an operation outside of normal firing checks and could compromise the readiness of the mortar. Additionally, the notion of no overhead clearance contradicts safety protocols, as overhead constraints can pose a significant danger during mortar operations. Thus, ensuring that the selector switch is correctly set is an essential and valid part of pre-firing procedures.