In the aftermath of the armistice on 11 November 1918, the first priority in the ‘zone des armées’ was to rebuild the shattered villages and fields and then, before very long, to plant them with hundreds of neatly laid out cemeteries and monuments. As far as ‘The Art of War’ was concerned, the next development after that was the building of the Maginot Line (see Fortress 010: The Maginot Line 1928–45 by William Allcorn, Osprey Publishing Ltd: Oxford, 2003) on the newly restored Franco-German border, as well as certain other modern concrete forts designed to protect Holland and Belgium from any further German aggression. Clearly nothing had happened in World War I sufficient to persuade governments that such works had become obsolete, although Fort Eben Emael on the Albert Canal will be best remembered by historians because it was so spectacularly captured on 10 May 1940 by two innovative new technologies: not only airborne envelopment, but also the use of shaped charges by assault pioneers to pierce thick concrete structures.
As far as fieldworks are concerned, the experience of World War I was generally accepted as the ultimate peak to which the art could possibly attain, and it was enshrined in the manuals of all the armies concerned: for example, the British Manual of Field Works (all arms) of 1925 essentially repeated the same advice as had its predecessors of 1917–18. The result was that when it came to the next world war in 1939–45, almost all of the practices used in 1914–18 were pretty well repeated verbatim. The main new addition was a burgeoning carpet of contact mines, both anti-tank and anti-personnel, which perfected the hesitant initial experiments seen in the earlier conflict. There was also an increased emphasis on personal slit trenches and foxholes, with correspondingly fewer deep shelters for large-scale occupancy, which was perhaps coincidentally accompanied by a general lightening of the weights of shell being used by the heavy artilleries. It nevertheless remained true that long sequences in the Spanish Civil War, World War II and the Korean War were fought out as trench stalemates, and with several continuous lines of trenches deployed in depth, very much on the model of the Western Front in 1914–18. Indeed one major US endeavour in Korea was codenamed ‘Operation Killer’, because it was designed specifically to maximise the attrition of enemy manpower. After Korea the wars tended to be less formal and set piece, with greater emphasis on light or guerrilla forces. Nevertheless, the siege of Dien Bien Phu in 1954 was a highly conventional trench battle, while the notorious tunnels of Cu Chi in the late 1960s must have been more than a little reminiscent of the Hangstellung of the Hindenburg Line.