Back to the Army;
I wonder what kind of batteries the Army would have to repulse a fleet.
From Striker: "Planetary defenses are of two types: active and passive. Active systems are designed to inflict damage on enemy starships attempting to bombard the planet or land troops, while passive defenses limit the ability of enemy forces to inflict damage on the world.
"The most common form of active defense is the deep meson gun site. A deep meson gun is a meson gun of ship ordnance size burried in a deep underground chamber. As the planet itself is transparent to the meson beam, the meson gun can fire at any target desired, while the site itself is effectively impossible to locate. Only when the gun site's surface sensors and target acquisition devices have been destroyed or captured can the gun be silenced, this generally requiring the use of ground troops or extensive planetary bombardment. At lower tech levels, laser and missile sites are used as well, but are much less effective and more vulnerable.
"Passive defenses center on major population concentrations, and take the form of damper projectors and large (city-sized) meson screens. The atmosphere of a planet itself provides an effective shield against long-range laser and particle accelerator fire, although vacuum worlds lack this protection and thus generally surrender if an enemy bombardment force penetrates it s system defense boats."
Invasion Earth presented a number of planetary defense troop units of corps size (100 batallions), division size (20 batallions) and regiment size (10 batallions). According to IE: "PD units are collections of energy weapons and missiles capable of engaging naval units bombarding the surface of a world. Each has an instrinsic garrison assigned to it; hence, a PD unit is rated and treated similarly as a troop unit. Most PD units are large, static installations and are immobile, while a few small PD units are mounted on grav vehicles."
Their basic function was to strike back at fleet elements that tried to bomb the world surface. They struck at full strength against ships on bombing runs (within 3 hexes - about 1200 km - of the unit) but only half strength against ships in the close orbit box, and they couldn't reach the far orbit box (which included the moon). The divisions and corps were fixed, couldn't be moved once placed: they represented fixed installations of some sort, possibly deep meson sites - defended by ground forces of the indicated size, of course - and would be parked near high-value targets like the starports or big cities. The regiments were grav-mobile, presumably mounting missiles since that would be easiest for a vehicle-mounted surface-to-orbit weapon - wouldn't need to carry the kind of power that meson weapons need; being mobile, they tended to get used to defend troop concentrations as the troops moved about the board.
The troop units themselves, even the field army sized units, did not have a surface-to-orbit attack capability - at least, not one that was significant in game terms. They depended on the PD units and SDBs, which made a certain amount of sense because the scale of firepower of even the little mobile PD regiments were on the same rough scale as an SDB squadron or cruiser squadron, and a PD corps could match a couple of battle squadrons. Doesn't mean the larger troop units didn't have some small organic surface-to-orbit artillery contingent, say something big enough to persuade a destroyer or two to think twice. Does mean, for the purpose of that game, that it wasn't enough to play a significant role if a cruiser squadron showed up.
Particle beams wouldn't work. According to the game, they can't punch through atmosphere. I've not the foggiest if that's true or not.
