Dean goes back in time, again, in the episode 11×14 of Supernatural, titled “The Vessel”
*Slight spoilers for season 11 of Supernatural* Castiel is back! Well, okay, not exactly. Lucifer is back in the Castiel meat suit, and the Winchester brothers are still none the wiser. And in this episode of Supernatural, titled “The Vessel,” we see that Dean somehow ventures back in time to 1944 to find a lost item. But while Dean is on his next quest, Sam is doing what he does best, researching information, this time with Lucifer, who’ll no doubt be playing his charade to his advantage.
Hoping to find a weapon powerful enough to defeat Amara (guest star Emily Swallow), Dean (Jensen Ackles) convinces “Castiel,” (Misha Collins) who is still Lucifer, to send him back in time to the last reported sighting of the Hand of God. Lucifer sees the potential in getting his hands on this weapon so goes along as Castiel and sends Dean to 1944 to the fated submarine mission that sunk the Hand of God. Meanwhile, continuing his charade with Sam (Jared Padalecki) while they wait for Dean’s return, Lucifer plans his next move.
Source: The TV Junkies