Ratbarf wrote:
Hmm, how about moon artillery? If you put a Rail Gun on the moon it would be damn hard to hit but rather easy to fire out of.
That's a very good idea that has been explored in the awesome sci-fi book "the moon is a harsh mistress" by Robert Heinlein. There are lots of other good things in that book (clever relationships for example), besides the obvious fun of dropping rocks from that height :-)
In a similar vein. If a gun is placed at one asteroid in the asteroid field (in our solar system then) and then uses the sun and/or a planet or two to slingshot their payloads to their targets, it will be very hard to retrace the trajectory with enough precision to find the right asteroid to hit, while it is not at all as tricky to gain precision enough to hit the right planet. This could be considered a mobile gun emplacement since the asteroids are not stuck in place, but it would be an uncontrolled mobile. Same situation with two planets firing shots at eachother. Pretty much every shot will hit the intended planet, but pretty much every shot will miss the exact gun emplacements. Having guided missiles will not make it much more likely to hit the gun emplacement. This makes sense because the guns will only stop firing once there is no point in defending anything anymore, since everyone is dead, and it assumes there is very little interest in keeping material values on the targeted planet. Of course there would be the alternative that a spaceship with guns could be counted as "mobile artillery" and could take out the enemys gun emplacements.
Lanrak: I'm not quite sure about that similar rate thing. Mobile defensive capabilities have pretty much lagged behind capability of doing damage, but static defensive has sometimes has a pretty good lead, wich caused starvation tactics and wars of attrition rather than victory by force. But mostly I think the power level fluctuates as new technology is improved upon. For example: the foot knights where the apex of late medieval fighting. They had such good armor that they didn't even bother carrying a shield. They went out of style quickly once the gunpowder came around and turned fighting much more mobile and/or alpha-strikey.