Was the WWI U-boat a death trap?

Delve into the world of WWI submarines with this online article by Matthew Seligmann for BBC's iWonder guides. iWonder is an archived series of online articles from BBC, intended to provide "thought-provoking answers to fascinating questions sparked by BBC programmes, the news, anniversaries and world events." Each subject contains videos, infographics and articles, though video content is region-locked.