About that shield thing, there is (IIRC) evidence supporting GTVA forcefield experiments in the blurb about the MX-50 (that bit about how it was ineffective against the Ross 128 energy array, or something). Maybe the hangar field is an ancestor or descendant of that particular line of tech. For all we know, the GTA might have been able to crack combat-effective energy shielding for small craft without Shivan technologies, via that tech. Could explain why they managed to pick up on shielding so quickly, they already had the fundamentals for it, they just couldn't build it strong enough to be viable for combat or so.