Washing a 1960s steel canteen cup in a dishwasher is not recommended. While steel canteen cups are generally durable, the high heat and strong detergents used in dishwashers can potentially damage or corrode the cup over time. Additionally, the dishwasher's agitation may cause dents or scratches to the cup's surface.
It is usually best to wash a steel canteen cup by hand using mild soap and warm water. Gently scrub the cup with a sponge or soft cloth to remove any residue, and rinse it thoroughly. After washing, allow the cup to air dry completely before storing it.
If you're unsure about the specific care instructions for your 1960s steel canteen cup, it's always a good idea to consult the manufacturer or seek guidance from experts in vintage or military collectibles. They may provide more specific instructions tailored to the cup's material and age.