AN: And now we get to the shields, and what I've been saying when I say 'Type *insert number*'.
UNSC/SGC Codex
Compiled by Dr. Catherine Halsey and Colonel Samantha Carter.
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Codex Entry Four: Energy Shields
Types of Energy Shield:
To date, the UNSC and SGC have encountered three definitive types of Energy Shield systems.
Type 1:
Also known as a 'Bubble Shield'. A Type 1 shield forms a bubble around its source, giving 360 degree coverage, and keeping fire away from the hull of a ship. This type of shield is designed to take rapid-fire from multiple directions, and thus, does not have 'zones' that power can be directed to. The entire shield is powered from the same source, and loses power at an even rate. A sufficiently powerful attack can render the shield useless, though more power increases the strength.
Examples: Goa'uld, Asgard
Type 2:
Also known as a 'hull-hugger', a Type 2 shield is subdivided into 'zones' spread over a ship's hull. Unlike a Type 1, this shield is designed to take heavy impacts, and redirect the damage across the whole shield, while power is directed to the damaged portion. However, enough powerful impacts in rapid succession can down this shield very quickly, e.g. the new model MAC aboard the UNSC Pillar of Autumn or Goa'uld Staff Cannons.
Examples: Covenant, Forerunner
Type 3:
The 'barrier shield' sub-type. Similar in appearance and function to the Type 1 shield, there are key differences. A barrier shield is also designed to take many impacts from multiple directions, with the major difference in how it does so. Where a Type 1 will slowly lose power (percentage of shield strength), a Type 3 will stay at full power as long as its power supply holds out. The only way to negate this is with a very powerful and focused attack, such as an Asgard Plasma Beam, or by shield-bypassing technology like an Ancient Drone.
Examples: Atlantis, Ori
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End Entry Four
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Redirect to Entry Five: Asgard
AN: My reasoning here is rather simple, and explained in the chapter. When one looks at Stargate/Halo, three types of shields pop to mind (at least on ships). The Goa'uld and Asgard use a shield that can take a bunch of rapid-fire shots, and slowly gets knocked down by percentage. And a sufficiently powerful (Ori) attack can pierce it in one hit. It also explains why Staff Cannons work the way they do...they are designed to take down a Type 1 shield, since the Goa'uld can't make a weapon strong enough to do it in one hit.
As for Type 2 shields...the Covenant and Forerunner use a 'hull-hugging' shield, that seems to be quite fundamentally different in design. It can take large impacts (MAC shells), though a large enough one (Super MAC) can still get through. It, however, is very vulnerable to rapid-fire hits. That's why the Pillar of Autumn is so effective against them.
And finally...Type 3 'barrier shields'. If one looks at Atlantis and Ori ships, it seems like they can't be brought down by conventional means, so long as they have power. Just look at Atlantis...they never say 'it's down to *insert percentage*!'. It's always 'the shield will last for *insert number of hours/days/weeks*'. The Ori shields seem to function the same way. The only way to get through this type of shield is a LOT of concentrated firepower, or a condensed attack like a Plasma Beam.