Youtube "UCAP Sandpit Amphibious assault" , they sometimes run milsims and have had an amphibious insertion before ( the site has a lake in it ) which was pretty cool.
I've seen sites that offer air, mortar or arty support via radio, the idea being you radio command, then this is passed onto marshal I am presuming, who then either pop smoke, or wait for targets to be designated via smoke before setting off pyrotechnics and declaring everyone within a certain radius or not behind certain cover dead, dependent on the support used or if they decide something was a direct hit on a bunker.