The Aegis Shield is a defensive system seen in Trinity Blood.
The Aegis Shield is a powerful magnetic shield created by the Methusalah. It was capable of protecting a ship from enemy weapon fire. To accomplish this, the shield worked to protect a ship at all angles, however, a problem arises as the shield prevents the ship its protecting from firing.
In order to fire at the enemy, the shield needs to be deactivated. Deactivation and reactivation of the shield takes less then a second with only the front and underside of the ship being exposed to enemy fire.