The Prat-kar is a Void Ship - a ship designed to travel through the Void. Technically it's not supposed to exist, yet what we see here proves the opposite.
As a Void Ship, it possesses a few useful features; its hull is very strong (it needs to be, to stand the immense anti-pressure of the Void), and it is very hard to teleport into.
Everything else known about the ship, its crew, and its role in the story, was lost in the Great Dataclysm.
- The Prat-kar's appearance is that of a Jem'Hadar battle cruiser in Star Trek: Deep Space Nine.