Trench warfare
Trench warfare occurred when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage. On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, camouflaged trapping pits, and other obstacles. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.
Cecil Vandepeer Clarke
When production of the limpet mine was under way, Clarke started work on a radical and ambitious project. Drawing on his experiences of trench warfare in the First World War and his particular expertise in tunnelling and explosives, he drew up a proposal for an armoured trench-forming machine. Although the war had started, there was little real fighting on the Western Front and this period became known as the Phoney War. However, Clarke reasoned that eventually Germany's much vaunted "Siegfried Line" must be attacked. His trench-forming machine would drive through the earth advancing 2000 yards in a single night, men and tanks following in its wake in the relative safety of the trench it had formed.