Had a similar experience in Nam. Charlie would figure where our artillery was and find a location that was unreachable from any of those bases; a safe zone, if you will. To offset this, when we'd discover their location, before daylight, we'd move a bunch of mobile 155s (the biggest at the time were 175s I think, so these were no. 2) 10 or 15 miles to the point where we could reach the bad guys. We'd then proceed to give them a wake up call.
I was a sound man on a motion picture crew filming this particular fire mission. There were more than 10, but less than 20, of the 155s. When they opened up, the earth moved, and I couldn't breathe for a few seconds. I don't think it aided my appreciation of music either.
