The specific mechanisms of this cover story needed to be consistent with what was known about aircraft crashes at sea. A man who had died in a crash might have died from the impact, from drowning, or from exposure. He would not necessarily show the specific marks of a crash, since a long fall into water does not leave the same marks as a crash on land. The important thing was that the body not show evidence of having been in cold storage for an extended period before being placed in the water, and that it show evidence consistent with time in the sea.
The question of how the body would be transported to the release point required the involvement of the Royal Navy. The original plan contemplated releasing the body from a submarine at a point where currents would carry it to shore. This required calculating the relevant currents and selecting the right location. The Spanish coast near Huelva was chosen because the patterns of ocean currents and coastal geography made it likely that a body released at sea in that area would wash ashore near the town. Huelva also had a significant German intelligence presence, through a network of agents and contacts operating under the cover of legitimate commercial or diplomatic activities.
The submarine chosen was HMS Seraph, a British S-class boat commanded by Lieutenant Norman Jewell. The Seraph had already been used for sensitive clandestine operations in the Mediterranean, including the secret landing of Allied agents and the transport of General Mark Clark for a meeting with French officers in North Africa. It was a boat with experience in unusual missions and a commander who could be trusted with the operational requirements.