Side project of Justin Vernon (Bon Iver) & Aaron Dessner (The National).

From their website:
In 2008, Aaron sent Justin an instrumental sketch of a song called “Big Red Machine” for Dark Was The Night. This was before they had met in person. Justin wrote a song to it, interpreting the Big Red Machine title as a heart. 10 years of friendship later, there are 10 more songs. Big Red Machine.