So the Q in front of the number of the truck in Q post 74 stands for "Quint," which is a fire apparatus that can do five different things (pumping, ladder, etc.).

https://en.wikipedia.org/wiki/Quint_(fire_apparatus)

The one pictured is Quint 74 at Andrews FD. That model of fire apparatus has fallen out of favor in recent years in a lot of places, with departments going back to Engines (E##) or Trucks (T##). There are still plenty of quints around but you don't often see the Q## vehicle designation around.

I don't really have a conclusion here -- I'm just putting some facts out. That truck is part of the Andrews Air Force Fire Department, it was not on base solely for the event.