I think it's pretty safe to say that this is a bag that the post office used to deliver mail to McDougall-Duluth Shipyards.

McDougall-Duluth Shipyards built ships for the government during World War I and World War II. The company was located on Spring Street in the Riverside neighborhood. It closed in the 1950s.

It was founded by Alexander McDougall, a seaman, captain and shipbuilder. He invented the whaleback, a lake freighter with rounded sides and deck. The S.S. Meteor is the world's largest whaleback, and is on display in Superior.

Definitely a cool piece of history. Where is this bag? Is it a family heirloom?