Alliance Cruiser
The I.A.V. Dortmunder is an Alliance cruiser. This cruiser stumbled upon the Serenity salvaging wreckage. Its commander decided to let Serenity escape in favor of helping a personnel carrier, which turned out to be a cry baby activated by Wash.
Behind the scenes
The name comes from the German city of Dortmund (compare the city of Hamburg and Hamburger).