1871–1914
Many fortresses built to defend both sides of the new frontier between France and the German-occupied provinces of Alsace and Lorraine, including the German ‘festen’.
1885–86
Aerial Torpedo crisis: HE shells are perceived as a major threat to extant fortifications. Fort La Malmaison (south-west of Laon) used as a test target for new French HE (Melinite) shells: it fails the test – so major additional protection is needed for selected forts at key sites.
1914
August: outbreak of war; reduction of the Belgian fortresses and deep German advances into northern France that were halted on the Marne.
September: the ‘race to the sea’ and the start of serious problems for the offensive: the Western Front is laid out more or less where it will remain until 1918.
1915
The year of deadlock and the disorganised improvisation of completely new tactics: mostly for defence, but also for attack. Many futile battles.
10 March: Neuve Chapelle – an innovative British artillery attack stimulates more German depth defence.
22 April: Gas first used in the second battle of Ypres.
9 May: Laffargue starts the concept of stormtroop tactics, at Neuville St Vaast.
1916:
21 February: 10-month battle of Verdun begins, leading to the sagas of forts Douaumont and Vaux.
1 July: The Somme starts – the Germans have a fully prepared battlefield, but they soon realise the weaknesses of their old ways and increasingly look to ever greater ‘depth’.
1917
23 February–5 April: Germans shorten their line by stepping back to the pre-prepared Hindenburg system along some parts of the Western Front.
16 April–9 May: Triumph of German depth defences against the Nivelle Offensive on the Chemin des Dames; but rather less success against newly co-ordinated British assault methods at Arras (9 April–16 May) and Messines (7–14 June).
July–November: Germans try successive new formulae for depth defence at Third Ypres, including widespread use of concrete structures.
November: Hindenburg Line breached at Cambrai – then the power of infantry counter-attack restores most of the lost ground.
1918
21 March: German offensives begin: show how little the British understand depth defence.
11 June: German offensives encounter French counter-attacks.
8 August: British offensives start at Amiens against improvised German defences.
September: British breach the Hindenburg Line. US offensive against the St Mihiel forts.