What is the sustained rate of fire for the 81mm mortar?

The sustained rate of fire for the 81mm mortar is defined as the maximum rate at which the mortar can be fired continuously for an extended period without causing overheating or mechanical failure. In this case, the correct answer indicates that the mortar can sustain a firing rate of 15 rounds per minute under these conditions. This rate allows for effective and continuous bombardment of enemy positions while ensuring that the equipment remains operable over time.

Understanding the sustained rate of fire is essential for planning and executing fire support missions. It ensures that units can provide reliable and sustained fire while managing the wear and tear on the mortar system. The other choices reflect various rates but either exceed operational limits or do not align with established capability for sustained performance, which is why they are not correct in this context.