A Vulcan starship sent into the Delphic Expanse whose crew went violently insane, and whose final transmission Soval showed to Archer in 2153 as a warning.
The Vaankara is a Vulcan ship that entered the Delphic Expanse some time before Enterprise did. It appears, through recorded images only, in the episode The Expanse.
After the Xindi attack on Earth, Jonathan Archer asks to take Enterprise into the Expanse to find those responsible. Ambassador Soval tries to dissuade him by playing the last transmission received from the Vaankara. It shows the crew, their emotional control gone, attacking and killing one another soon after entering the region.
Archer goes anyway. In the later episode Impulse, Enterprise finds a second Vulcan ship, the Seleya, in the same condition, and T'Pol traces the madness to the mineral trellium-D.