Umbras main reason for going so far from Terra was to be able to work on technology on their own without Adeptus Mechanicus looking over their shoulder all the time. When Abaddon launched his first Black Crusade Green Shadows were one of the first Space Marine Chapters to be on their way. But they were first contacted by the Iron Warriors Legion promising worldly things for Green Shadows to align them with Abaddon and the Chaos Gods. Umbra knew of Iron Warriors technological advance and he lead his soldiers against the imperium they had served for hundreds of years. Green Shadows lead their advanced fleet to near-by systems with Imperial Guard feeling secure as the traitor legions got closer but at least they had their own marines to protect them. When Umbra unleashed his attack on the unsuspecting Imperial Guard down on the planets the soldiers were without leaders as the space marine strike forces had first attacked the leaders of the army. It was withing one month that Green Shadows had a whole solar system all but massacred to the last man and child. Gaining control of the solar system got the attention of other space marines. Salamanders were the first to act against their now fallen brothers. Salamanders lead out a campaign against Umbra's Green Shadows the battle didn't rage for long as Umbra knew himself to be overnumbered and they soon fled from the solarsystem to aid Abaddon, but the first Black Crusade was over and the Chaos forces were on retreat. The Green Shadow fleet followed the Iron Warriors to the Deamon World of Medrengrad. The Fleet orbited the planet. The first sign of Green Shadows pact to the Chaos Gods was Umbras accent to Deamonhood as a new Deamon Prince. He warped the captains quarters in the fleets flagship Umbra Triremis into his own domain where he stays for most of the time only leaving to assault the enemies of the chapter in a bloodlust driven by the Chaos Gods themselves.