Sadly this isn't a recently discovered super power to repel enemies with sound, it's more to do with what happens when you break the speed of sound.
Sound waves are created at finite speeds. So a sonic boom arises when an object such as a plane is travelling faster than the sound it generates.
In the plane example, the sound waves propagating at the front of the aircraft stack up under the pressure from the aircraft moving so fast against them into much bigger and louder sound waves.
It's usually easier to imagine a boat and a smooth, still lake. If a boat drives full throttle in the water then a build up of waves occurs, into one bigger wave at the front of the boat as the water tries to get around the boat itself. This is the same for aircraft with the air being like the water in the boat example.
So this intense build up of sound waves at the front of the aircraft create a sonic boom as the bigger clusters of sound waves try as quickly as possible to break past the plane, making a tremendous sound.
However if you see a plane breaking the speed of sound coming towards you in the sky you won't hear anything until the plane passes overhead. This is also due to the doppler effect.
Now the speed of sound does vary with temperature. Use the search bar to find out more answers to interesting sound questions and phenomena.
Thanks for reading and here is a video of what a sonic boom looks like: