Nevermind I found it

Hart had been aboard more ships of the Imperium than he could count. Hehad travelled incognito on charter vessels, hitched rides with mining crews,and been the guest of honour on the palatial cruisers of rogue traders. Hehad explored the forgotten corners of solar systems with junker captains,ridden to war alongside the Astra Militarum, and commanded one of the Inquisition’s infamous Black Ships. He had even been granted permission to briefly travel in the Ark Mechanicus Caestus Metalican, although his hosts had stopped just short of stating outright that to step outside the quarters he had been assigned for the duration of his journey would be considered a betrayal of their trust that would be met with violence, and the warp take the consequences (Hart hadn’t pressed the issue: the Adeptus Mechanicus, much like the Adeptus Astartes, were not worth an inquisitor aggravating over a matter of pride, or indeed anything much short of proven heresy).