From Halopedia, the Halo wiki
The most famous UNSC hospital ship was the UNSC Hopeful, a massive medical research facility and mobile hospital made of two refit stations welded together. It was considered legendary throughout the UNSC and virtually always on the move. The Hopeful was the site of the SPARTAN-III augmentation procedures. A similar station, Medical Facility Endurance, was used to administer the SPARTAN-II augmentations.
The Covenant also made use of hospital ships, which are used to provide medical support to the fleet's entire complement of personnel. Such vessels were employed in the Fleet of Inexorable Obedience, as part of the fleet's logistics and supply train. After several days of observing the Covenant's logistics fleet at Etalan, John-117 still found it difficult to distinguish the Covenant's hospital ships from their munitions carriers and equipment freighters.