Battle of the Nibelung Rings

The Gas giant Planet Nibelung, in the Midgard System, the 501th Imperial Marines stationed on the Wotan moon Outpost are trapped and without support against the Zidrii fleet's bombardment.
This massacre is one of the worst defeats in the Empire's History and the first time an Apocalypse-class (HMS Kraken SCVN 806) was destroyed.