Seabourn has unveiled details of the submarines that will be offered aboard its expedition fleet from 2021. Seabourn Venture and her yet-to-be-named sister-ship will each carry a U-Boat Worx Cruise Sub 7 submersible, an underwater battery-powered craft that will take up to six guests to a depth of up to 300 metres below sea-level. They have been “designed specifically for Seabourn,” the cruise company said.