Submarine is serving as Dutch co-producer on Pieter-Jan De Pue's new feature documentary, Mariinka, which will have its world premiere as the opening film of CPH:DOX and will subsequently screen during Movies That Matter. Originally titled "Four Brothers," the film follows young Ukrainians caught up in the war with Russia in various ways, with the 2022 Russian invasion shifting the focus from four brothers to new characters like medic Natasha and smuggler Angela. Submarine previously collaborated with majority producer Savage Film on "The Land of the Enlightened," while the Netherlands Film Fund financially supported the project despite significant delays due to the dangerous filming conditions in Ukraine.