S2 Energy Shield

The S2 Energy Shield was the first effective energy shielding system to be used on vessels of the UNSC Navy. Introduced in 2564, the S2 was engineered by government-sponsored research agencies and borrowed much of its technology from captured Covenant material. However, the S2 could sustain far less damage than its Covenant counterpart; nevertheless, it was essential in safeguarding against lighter hostile weapon systems.
A unique innovation not seen with Covenant shielding was that it relied on a series of triangular energy panels (approximately 75-100 panels) which interlocked to form into an elliptical bubble around the vessel. Various panels could be deactivated to allow outgoing weaponry to be fired. The panel could then reactivate and be brought up to full strength within thirty seconds.
In 2573, a prototypical yet shockingly practical second version was introduced to the Navy. It was initially allotted to vessels of the AdWarFleet, though within five years it would be standard equipment on nearly sixty percent of UNSC ships of the line. The primary innovation seen with this second iteration was a much shorter recharge time as each panel now required no more than eighteen seconds to recharge.