USS Darwin-A Hull Plating
As the Federation and Starfleet recognise that science ships cannot always remain out of combat, it has a thick anti-phaser plating which assists the shields in defending the ship from energy-based weapons. While no armour in the Federation that is impervious to phasers exists and damage would still be taken should a phaser blast penetrate the shields, this reduces the chances that whatever may be housed in the containment sphere could be ignited, or find its way through the ship’s hull.