The correct answer is B) readily accessible locations. Life jackets must be stowed in readily accessible locations, as per the US Coast Guard regulations. This ensures that they can be quickly retrieved and put on in the event of an emergency, allowing passengers and crew to rapidly don their life jackets. The other options are incorrect because: A) survival craft is too specific, as life jackets should be accessible throughout the vessel, not just in survival craft; C) locked watertight containers would make the life jackets difficult to access quickly; and D) mess rooms are not an appropriate stowage location for life jackets.