Gil Hamilton wrote:The Rebel's snowspeeders didn't get fried by the Hoth shield when they went flying around looking for Luke and Han, or for that matter the floating probedroid that not only entered the shield but got close enough to the shield generator to take a picture of it to broadcast back to Vader. They may have lowered the barrier for the snowspeeders, but they sure wouldn't have lowered it for the probedroid. Or the assassindroid in AotC that was sitting right next to the shield protecting Amidala's room without getting zapped by an electrical discharge.
Walkers are special Marine armor allowing for attacking planetary targets where theatre shields are in place. Air support and respulsor vehicles are ruled out--the higher repulsorlift vehicles fly, the worse they'll suffer from discharges from the extreme charge gradient between the
shield rim and the ground beneath it.
A base with a theatre shield can mine all the navigable-ground approaches which are situated beneath the shield's edges. Very-low-flying repulsorlift and tracked or wheeled vehicles will be routed by enemy defenses in the minefields. Higher-flying repulsorlift vehicles and aircraft will complete a circuit between the tactical theatre deflector shield in the upper atmosphere and the planetary surface. Needless to say the discharges plaguing aircraft and high-flying repulsorlift vehicles will be vastly more severe than lightning caused by thunderheads.
An example of this would be the turbolaser and ion cannon bombardment of the tactical theatre shield at Blackmoon in
X-Wing: Rogue Squadron. The energy intake of the shield raised the charge gradient so much that energetic discharges randomly leapt groundward from the shield's edge to trees and other normally insufficient conductors, starting massive forest fires. Another is
X-Wing: Wedge's Gamble, with absurd electric storms and energy discharges on Coruscant, as well as energy leaping between shield interfaces when one was opened to allow Loor's shuttle in.
Beneath the shield, the shield itself forms a protective barrier against charge gradients just as deflector shields do against ion cannons. Therefore repulsorlift vehicles and aircraft function just fine under the protective shield--it is only at the shield's edge where the charge gradient is exposed to the ground by the shield's termination that the discharges are possible.
Walkers' feet and legs are more easily armored than the entire chassis of tracked and wheeled and low-flying repulsorlift vehicles, and have a much smaller foot area, decreasing the likelihood of mine detonation. And even if the mine detonates, the main body of the vehicle is raised to where armoring against kiloton-range mines is practical. The legs and feet ground the vehicle, preventing the disastrous discharges at the shield perimeter.
In order to overcome these obstacles conventionally, extremely heavily-armored repulsorlift vehicles may become necessary, or heavy area-effect weaponry to clear mine-fields. This may well have been standard practice for the Republic and later the New Republic, and perhaps even the Imperial Army against conventionally-armed foes. However, the primary late-era Republic and Imperial foes with non-planetary theatre shielding were poorly-equipped insurrectionists/successionists and Rebels, respectively.
The Grand Army, and later, Marine philosophy probably dictated that a rapid push against inferior enemies using highly-expensive, highly-specialized walker armor manned by elite, and superbly trained crews and supporting troops of the same quality (this explains why walkers are new in a technologically stagnant galaxy) in lieu of slow and costly means such as superarmored repulsorlifts (which due to repulsorlift limitations becomes more problematic with increasing mass and thus armor, and easier targets for anti-starship weaponry) or minefield clearing, which would also give the enemy greater time to escape. If you imagine the Hoth mission as a paradigm, the Imperial Marines needed the ability to quickly get under a theatre shield and knock out it out as well as other strategic defenses before the enemy could prepare for escape. Highly-specialized walkers not designed for extended combat or longevity against very poorly equipped enemies overcome many of the problems associated with "Mecha."
Imperial Army and New Republic Army forces in large-scale ground combat and occupation relied on standard repulsorlift vehicles and tracked and wheeled combat vehicles.
Gil Hamilton: the absence of atmosphere around the Death Star and spacecrafts negates many of the charged-particle issues associated with theatre shields.
The existance of extraordinary charge gradients caused by theatre shielding is a canonical fact from the AOTC ICS. The natural grounding prevents a gradient in charge developing within the vehicle itself, preventing the catastrophic discharges before they occur, similar to a lightning rod.
There is no oppurtunity for shields such as the Gungan tactical shield and the security shield at Senator Amidala's residence to create such charge gradients. In the case of theatre shielding, the charged particles isolated, created, and collected by the theatre shield are dozens of kilometers above the surface. The Gungan shield, does not confine thousands or millions of square kilometers of charged particles dozens of kilometers above the surface, as well as relying on different principles than standard shielding. The Senator's residence did not build up the same charges as well.
