Washing a 1960s US Army steel canteen cup in a dishwasher is not recommended. While steel canteen cups are generally durable, the high heat and harsh detergents used in dishwashers can potentially damage or discolor the cup. Additionally, dishwashers often involve strong water jets and agitation, which may cause the cup to scratch or dent.
It is best to clean a 1960s US Army steel canteen cup by hand using mild dish soap and warm water. Gently scrub the cup with a sponge or soft-bristle brush, paying attention to any areas with stubborn stains. Rinse the cup thoroughly and allow it to air dry. This method will help preserve the appearance and integrity of the canteen cup for a longer period.