How to train calf muscles to prepare for military training?

I suggest you practice the frog leaping duck step, all by the explosive force of your legs.

You can also kick sandbags.

Don't run at a constant speed all the time, run for a distance and then sprint. The more sleepy, the more sprint.

These are all affirmation of the explosive power of leg training, and can also turn your fat into muscle.

Don't practice in the gym. What you practice there is that the shape does not explode.