The Momsen lung, a primitive WWII rebreather for escaping submarines.

Fullsize image: https://diqn32j8nouaz.cloudfront.net...g_fullsize.jpg




Previously:

Transporting a submarine on a truck - GIF
Narco-submarine captured by U.S. Coast Guard - video and infographic
The H.L. Hunley, the first submarine to sink a warship
Submarine rescue chamber - photos
steam-powered submarine
Raising WWII German submarine U534 - videos
Guppy submarine torpedo room - photo