It’s primary purpose is to help to boost trade, but a ship can only be in one place at one time. We have embassies around the world, they would be better able to facilitate trade events using their facilities and local infrastructure. Britannia was first and foremost a royal yacht designed and built when Britain’s position in the world and Commonwealth was marked by Royal visits overseas. The world has moved on. I worked on the 1990s project fir a replacement to Britannia, but that first and foremost was a Royal Yacht. To my knowledge Britannia was never ever even excercised in a hospital or humanitarian role. Thee were other better ships available.
Here’s a picture of the late 1990s study. Electric propulsion too!
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