How the allies won the war in 1918: Strategic alignment or complete u-turn?

In 1918, Allied strategy was formed at the political/military level by formal conference, supported by a Supreme War Council (SWC). There had already been a strategic rearrangement at the turn of the year after disappointment in 1917. On the Western Front the combined ‘Nivelle Offensive’ and the British attack at Arras had failed, with the former resulting in French mutiny. Britain had to take the lead in offensive operations, but its main effort at Passchendaele was costly and unsuccessful. The year ended with a brilliant tank attack at Cambrai but German counterattacks recaptured the lost ground.

These failures were combined with momentous events elsewhere. The Italians collapsed at Caporetto in October 1917 and Russia was knocked out of the war by the Bolshevik revolution of November 1917. The only ray of hope was that the German unrestricted U-Boat campaign had induced America to join the Allies and convoys had reduced the damage that it was causing to the Allied war effort.

It was against this backdrop that the Allies developed their strategy in early 1918. The aim was to go on the defensive on the Western Front in the face of increasing German strength following the transfer of its forces from the Russian front. The Allies would await the arrival of American troops and abandon the offensive until 1919. The naval blockade of Germany would continue and Britain wanted to maintain pressure in Mesopotamia and Palestine against the Ottomans. This prolonged the discord between ‘Westerners’, such as the British Commander in Chief (CinC), Field Marshall Sir Douglas Haig, and ‘Easterners’, such as Winston Churchill. The former thought that Germany could only be defeated on the Western Front while the latter preferred to knock out the ‘props’ represented by the other Central Powers.

The Allied strategy was supported by underlying operational changes. In January 1918, Britain took over an extra section of the French line. Haig’s request for 600,000 troops to replace losses in 1917 resulted in an allocation of only 100,000 men by the government’s Manpower Committee. The impact contributed to the reduction of the number of infantry battalions in each division by 25%. The British Army would be facing the German Spring offensive with an extended frontage, covered by weaker divisions and limited reserves. Any hope that newly arriving American forces would fill the gap was scotched by an American policy to form its own army to fight under its CinC, General John Pershing.

The Allies did not have to wait long until the strategy and operational structures were tested. The first German offensive was launched on 21 March 1918 and fell on the newly extended frontage held by the British Fifth Army, threatening the junction of the British and French armies. With defences incomplete, and few reserves, the outnumbered Fifth Army collapsed. Haig called on the French CinC, General Petain, for promised French reinforcements, but without an Allied general reserve the response was neither fast nor weighty. With fear of a split between the Allied armies, a crisis conference was called on 26 March 1918 at Doullens.

The result was the appointment of General Ferdinand Foch with ‘coordinating authority’ for Allied military operations in France, powers that steadily increased to become Allied Generalissimo. Haig performed a U-turn on centralised command by being one of Foch’s strongest supporters. Subsequently, the duo enjoyed a relationship that became one of the biggest factors in Allied victory. When the Allies managed to get on the front foot in July 1918, Foch’s method of coordinated blows at different parts of the front represented war-winning operational art. Haig happily obliged by mirroring the method with his five British armies.

U-turns multiplied in response to the German offensives. Britain transferred two of the five divisions that had been sent to Italy. The campaign in Palestine and Mesopotamia was ‘indianised’ by replacing British divisions with their Indian counterparts, who were ideal troops for the Middle East. The British war cabinet acknowledged its mistake in restricting manpower and began to flood France with battle casualty replacements (BCRs). This was to replace the high casualties from the German offensives and bring other divisions up to strength. In the first quarter of 1918 only 176,101 infantry and cavalry BCRs had been supplied but this increased to 318,746 in the second quarter and 244,948 in the third.

The French Army was also forced into a U-turn, playing a bigger and earlier part than Petain expected, as divisions were fed in to support the British Army. Ironically, the junction of the French and British Armies in April 1918 was due west of the original point occupied before the British extension in January 1918. With the French line becoming thinner, pressure also gathered on the Americans to play an earlier part than planned.

Pershing’s wish to fight as an army was compromised when he responded to the crisis by offering five American divisions to take over part of the French line. American support expanded when the French faced the third German offensive. Three American divisions were blooded at Cantigny and Bellau Wood. Two divisions fought under the British in the ‘Advance to Victory’. Otherwise, Pershing had his wish to fight as a separate entity in the Allied forces. American attacks at St Mihiel and in the Meuse-Argonne took place in September 1918 and American forces played a full part until the armistice. Of the two million troops in France, 1.4 million were engaged in combat. Thus, America had also made a U-turn by engaging most of its army before 1919.

The American attacks were part of Foch’s blow-by-blow methods, which began immediately after the fifth German offensive was defeated in mid-July 1918. The French went onto the offensive on 18 July at Soissons. The British followed at Amiens on 8 August and the tempo of successive attacks kept the German Army off balance. With Germany wobbling on the Western Front the pressure grew on the other Central Powers, who could no longer count on German support. The Ottomans buckled in Palestine and Mesopotamia. Austria-Hungary was steadily forced out of Italian territory, while Bulgaria was also thrown back into Serbia. All of them sought an armistice before Germany came to the table. The Westerners had been right, fatally weakening Germany on the Western Front knocked out the ‘props’ in the Central Powers.

The Allies had faced challenging circumstances, but this had not forced a strategic U-turn. The U-turns were made at the operational level and these formed the building blocks of a strategic rearrangement. The Allies revised their command structure; the British had been forced to reinforce the Western Front rather than pursue manpower restrictions and ‘Eastern’ gains. The French had to engage its forces en masse sooner than expected after the 1917 mutiny; the American Army had engaged in combat far earlier than its experience warranted. The Allied strategy of staying on the defensive in 1918 had turned into an offensive on a grand scale. The German Spring offensives had unwittingly caused an Allied strategic rearrangement leading to Germany’s defeat in November 1918.

This piece is part of a series of blogs produced by scholars from the School of Security Studies Military and Political History research theme.

Glyn Taylor is a PhD Researcher in the Defence Studies Department, School of Security Studies, King's College London.