It was a foggy night but there was definitely a Chinook helicopter in operation off Swanage.
A quick check on AIS showed the ' Hartland Point' also off Swanage.
These ships are used to ferry military equipment around the world.
So was it a coincidence that a ship, a big helicopter , some Royal Marines and then large bangs may indicate an exercise?
The sister ship to Hartland Point is called Anvil Point by another coincidence !