The Vessel
S11, E14: Hoping to find a weapon powerful enough to defeat Amara, Dean convinces Castiel (who is still Lucifer) to send him back in time to the last reported sighting of The Hand of God. Seeing the potential in getting his hands on the weapon, Lucifer goes along with the plan and sends Dean to 1943 on an ill-fated WWII submarine mission that sunk with the artifact. Meanwhile, Lucifer plans his next move, while maintaining the Castiel charade with Sam while they wait for Dean's return.
