Blueunicorn6, you have it exactly correct! The three legs of effective mortar fire is, Gun Line, Fire Direction Control and Forward Observer.
I believe this was pre-planned and obviously incorporated all the tenants of a professional indirect fire team.
A great question would be: Did they have a Fire Support Coordination Cell which would imply that it was a battalion sized supported operation? You can bet that someone has the communications, at minimum, from the FO to FDC or Gun Line.
Yep. The scary part is thinking about who has that capability and who doesn’t.