Citizen Promaster Silver Tank Case, which is a specialized watch storage and display box designed to resemble a scuba diving tank.  Key Features Design: A unique, "tank" shaped holder used specifically for Citizen's Promaster line of diver watches. Usage: It serves as both protective packaging and a display case for collectors. Availability: These cases are often sold as part of a "Full Set" with a watch, but can also be found as standalone empty storage units.  Popular Compatible Models While many Promaster watches use this style of packaging, it is frequently paired with: Promaster Diver 200m (e.g., model NY0125-83E). Promaster Dive Eco-Drive (e.g., Orca or Professional models).