Artillery Delays

[CStock88]

This actually might come up in my campaign, as the PCs are still apart of a functioning infrastructure (at least, so far!). The PCs have been assigned the role of acting as FOs for the rearguard that's in place to cover the retreat of the larger organization they're apart of, due to the fact that normally they are in the role of a scout unit. All other things being equal, and the division's actual FO crews dead by this point, the PCs might be able to pull it off... (of course, it won't be as easy as "just" waiting to call in the fire mission; enemy infantry seeping through the thinly held line, ahoy!)

Artillery. Assuming a company commander requests a fire mission, and assuming that he has, say, a couple of gun tubes allocated to him, and he calls in a fire mission (or the FO calls it in, or whomever)... is it likely that said fire mission will take a long time? And if so, what would a long time possibly be? A half hour? Twenty minutes? I'm kind of wondering to see how much suspense I can fit in, as they watch the five surviving Soviet tanks advance, effectively unopposed, as the rest of the unit's immediately available anti-armor ammunition is already considered expended at this point.

I'm assuming that if the place he wants the shells dropped is pre-planned and approved by the FDIC (or whatever makeshift organization is there to take its place!), the time would be significantly cut down. I'm also assuming that once the artillery makes a fire mission, it's going to pull up stakes and run like hell, probably because their shells are rather limited, not to mention wanting to avoid any return fire. (I actually might have them run out of rounds, forcing the PCs later on to haggle at a friendly depot, or something, to get some more).