Ultramar Campaign, 999.M41
Upon learning that Maccrage itself was besieged by hordes of Chaos Marines, Chapter Master Valerdin called upon the 9th, 4th and half of the 1st Companies- every other Astartes being tied up elsewhere in the galaxy to rendevous with the survivors from the 2nd Company and the other half of the 1st Company at Maccrage to provide relief to their Progenitor Chapter.
By the time they had arrived, Guilliman had awoken from his slumber and was launching a counter offensive to reclaim the 500 worlds. The glory and honour of fighting alongside a Primarch was not to be missed by the Tempest Angels, as they spent the following months fighting with such inspired courage that they received praise from the Primarch himself.
At the end of the campaign when news reached Valerdin of encroaching forces on Astoth, he begged the Primarch's forgiveness for his departure to defend his Chapter's home world and left the 2nd Company- now down to just under half effectiveness in addition to 100 Scouts under his command as he took the rest of his force to Astoth to relieve the planet from invaders.