A class of Starfleet transports and tugs built in great numbers at Utopia Planitia for the armada meant to evacuate Romulan space before the supernova, and destroyed in the synth attack on Mars.
The Wallenberg class is a warp-capable ferry with a wedge-shaped forward hull, designed to move very large numbers of people. It was the backbone of the rescue armada Admiral Picard organised in the 2380s to carry some nine hundred million Romulans to safety.
The ships appear in the first season of Star Trek: Picard, in the flashbacks of Remembrance and Maps and Legends. On First Contact Day in 2385 the rogue synthetic workers at Utopia Planitia destroy the shipyards and the unfinished fleet with them, and Starfleet abandons the evacuation. In Absolute Candor the class is named as the type of transport that brought refugees to Vashti.