Real power in France in 1914 lay neither with the depressed and overwhelmed prime minister René Viviani, nor with the figurehead president Raymond Poincaré. The man who called the shots at the beginning of the war was Generalissimo Joseph Joffre, the supreme chief of all French armed forces, and later of British and Belgian forces as well.

In the run-up to war, Joffre reorganised the French army, extended conscription from two to three years, and adopted plan XVII (so-called because it was the 17th war plan devised since the 1870-1871 Franco-Prussian war.) He also consolidated relations with Britain and Russia.

Like many in the military, Joffre was steeped in Napoleonic tradition and believed l'offensive à outrance – the all-out offensive – would deliver victory over Germany. He had little understanding of modern warfare and underestimated the importance of artillery. In 1914, France had 280 heavy artillery pieces, compared to Germany's 848.

As the civilian government dithered, paralysed by the fear that France would be seen as an aggressor, Joffre began pushing in late July for military preparations. At his urging, general mobilisation of France’s 880,000-strong army – 3.6 million men including reservists –was announced on August 1st, two days before Germany declared war on France.

Joffre wanted to send French troops into neutral Belgium, but instead agreed to pull his forces 10km back from the border, at the insistence of the civilian government. The priority of plan XVII was to regain Alsace and Lorraine, provinces lost to Prussia in 1871. In August, Joffre attacked German forces in Alsace, Lorraine and the Ardennes in the "battle of the borders", but was driven back by the German counter-offensive.

August 1914 was a disastrous month, with more than 100,000 French deaths and virtually the entire army in retreat. Joffre ordered the execution of deserters and of all officers who showed “weakness or cowardice before the enemy”. He would sack 162 generals in the first five months of the war.

Yet Joffre initially bounced back. He owed his immense popularity, and the nickname "Papa Joffre", to the first battle of the Marne in September 1914 when French troops – some ferried to the front in taxis – routed the German advance towards Paris. He succeeded, too, in Flanders that autumn.

But hundreds of thousands of lives were squandered in Joffre’s futile offensives in the Artois, Champagne and the Somme. To his admirers he remained the victor of the Marne; to others, he became the butcher of ‘14. Heavily criticised, he was given a face- saving promotion to Marshal of France in late 1916 and replaced by Gen Robert Nivelle.

Joffre nonetheless continued to enjoy great prestige. He was sent to the US to enlist US support for the war, and was elected to the Académie Francaise. Joffre imposed his former deputy, Gen Ferdinand Foch, to prosecute the last months of the war. They rode side by side in the victory parade on Bastille Day 1919.