Which of the following is a key component of the 81mm mortar's pre-fire safety checks?

The securing of the cannon to the baseplate is essential for effective and safe mortar operation. When the cannon is properly secured, it ensures stability during both the firing process and in the moments leading up to it. This stability is critical because it allows for accurate targeting and minimizes the risk of unintended discharges or misfires. A cannon that is not securely attached could lead to dangerous and unpredictable outcomes, jeopardizing both personnel and equipment.

In the context of the other options, an unlocked bipod locking latch would compromise stability and safety, as it could allow for movement of the mortar during firing. A loose leg-locking handwheel would similarly pose a safety concern, potentially allowing the mortar to shift unexpectedly. A firing pin recess that is facing down does not pertain to proper pre-fire safety checks, as it is more about the design of the firing mechanism rather than securing components of the mortar setup.