We already know that Cargo Ships are used to transfer illicit substances: https://www.cnn.com/2019/07/10/business/jpmorgan-msc-gayane-cocaine-seizure/index.html What if intentional dumping of specialized, waterproof, tracked containers to the bottom of the sea was a way to transfer goods from one (extremely wealthy) party to another? You could write it off as an accident and claim any insurance on a shipment. No one is going to look around at the bottom of the sea, except for the people who you want to find the container.