The enduring image of World War I is of men stuck in muddy trenches, and of vast armies deadlocked in a fight neither could win. It was a war of barbed wire, poison gas, and horrific losses as officers led their troops on mass charges across No Man’s Land and into a hail of bullets. While these impressions are all too true, they hide the fact that trench warfare was dynamic and constantly evolving throughout the war as all armies struggled to find a way to break through the opposing lines.

Most books and documentaries about the war focus on the carnage of the trenches, depicting the ceaseless bombardment and sniping, and the assaults and counterattacks that took millions of lives. This was the experience of most frontline soldiers during that great conflict, but it was not the only experience. There was another war going on beneath the trenches, a war of tunnels and mines fought by men who didn’t see sunlight for days at a time and who lived in constant fear of cave-ins and enemy detection. These men, who had mostly been miners in civilian life, lived a twilight existence, working long hours in silence and near darkness while great battles raged overhead. They suffered from fatigue, stress, and the knowledge that they could be killed at any time by an unseen enemy. Despite this, they persevered, and the mines they laid under enemy trench systems turned the tide of at least one major battle.

Submarine warfare began tentatively during the American Civil War (though the Netherlands and England made small prototypes centuries earlier). Robert Whitehead's invention of the torpedo introduced the weapon later used most frequently by submarines. Steady improvements to Whitehead's design led to the military torpedoes deployed against shipping during both World Wars.