Exploding artillery drove fortifications entirely underground by WWII

Evidence

During the Battle of Britain in 1940, the safest shelters were the deepest ones, and because they were in short supply, as many as 150,000 Londoners huddled in a labyrinth of subway tunnels each night. The Maginot Line, an inordinately expensive, thousand-mile-long string of fortifications built by the French to stall and divert the advancing Germans, was almost entirely belowground. The Japanese carved elaborate networks of tunnels, gun ports, and barracks into the volcanic rock of the Pacific Islands. Shielded by solid stone, these positions withstood repeated bombardment from battleship artillery and bombs dropped by planes, and in the end most had to be cleared by brutal hand-to-hand combat. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 523

Categorization

• XREF: connects to: Explosive artillery ended the era of fortified structures above ground. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 974; Siege artillery evolved to exploit the fragility of fortress wall corners — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 513; Fortification style evolved in direct response to artillery effectiveness — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 972

Related

• Explosive artillery ended the era of fortified structures above ground. (similarity 0.86)

Broader Connections

• Explosive artillery ended the era of fortified structures above ground. #corroborates (0.90) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 974
• Fortification style evolved in direct response to artillery effectiveness #expands (0.70) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 972
• Siege artillery evolved to exploit the fragility of fortress wall corners #expands (0.60) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 513