They have fought more than just feral orks. I mean if anything they have fought regular orks more.
They have proven themselves, on more than one occasion. The Damolcles Gulf was just the begining of a number of victories they have had over the Imperium. Against the Orks, commanders like Puretide, and Farsight have made their names. Commander Brightsword showed his skill by defeating the vostroyans on Nimbosa. The have beaten back the Tyranids of Hive Fleet Gorgon and contained the Orks in the War of Dakka. The only race that they haven't won a real victory over is the Necrons (Because they are just a bit too trusting
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