Tech Levels

A bit OT but fun nevertheless. The best bit in any of Harry Turtledove's books
is when the Germans fire a railway gun at one of the landed alien spaceships.
The aliens pick the shell up on radar and think it is a missile (for what else
could it be?) and start firing anti-missile missiles
at it which have no effect on a piece of steel the size of a car. THe aliens
panic, an indestructable missile!