A century ago today was the mid-point of the third British Ypres offensive on the western front. It was not then popularised as the Battle of Passchendaele, because the taking of that pulverised former village (by Canadian soldiers) was more than six weeks away.

Ordered by King George V’s friend and working-class enemy commander-in-chief Sir Douglas Haig but carried out — with vast casualties — by his troops, the campaign began on July 31 (after 10 days of artillery bombardment) and was concluded on November 10, without any confession of guilt for another bloody failure.

Haig had believed that the German armies were close to breaking point, that attacks aimed at extending the Ypres bulge at the front would pierce the German lines, and enable the British armies to swing northwards and on to the Belgian coast.

This enormous misjudgment was not Haig’s first. Passchendaele was supposed to have been passed on the fourth day of advance. It was less than five miles from the starting point and was reached after almost 100 days of bitter struggle against mud-filled shell craters as much as against the armies opposite — armies soon to be strengthened by divisions released from an eastern front from which many Russian soldiers had already walked home.

The German forces had been given plenty of warning of the attack, while Haig and his confederates simply ignored the impact of shells on the surface of the land on which the troops were to advance.

The water table was almost at the heavy clay surface in this sector, and the initial British bombardment unsurprisingly turned the terrain ahead into a dark and murderous swamp — in which an unknown number of the “missing” drowned.

The total number of British and Empire casualties in this third Ypres assault amounted to well over a quarter of a million, including 62,000 dead.

The war, wrote A J P Taylor in his book The First World War, “did not need revolutionaries to make the war unpopular. Blunders by the generals could do that by themselves.”

The boneheaded Haig had learned nothing from the previous year’s Somme offensive, when the price of gaining seven square miles of land from the German armies had been almost half a million casualties (over 19,000 dead on the first terrible day), plus, as Taylor wrote, the loss of idealism amongst the survivors.

But Haig had too many military, political and royal friends to fear dismissal, and though prime minister and Liberal imperialist David Lloyd George could perceive Haig’s inadequacy, his priority was to minimise his own vulnerability.

Lloyd George did this by tolerating Haig, for a start, but also in other ways. Arriving in Glasgow to be awarded the freedom of the city on June 29, he was faced with a large demonstration calling for the release of socialist and anti-imperialist John Maclean, who had in spring 1916 been given a jail sentence of three years with hard labour. Maclean was released for anti-war service the next day.

Reduced war enthusiasm in summer 1917 found a symbol in a dramatic statement of a serving officer and published poet on convalescent leave in London.

This was second lieutenant Siegfried Sassoon, whose words first appeared publicly in Sylvia Pankhurst’s Workers’ Dreadnought on July 28 1917, three days before the third Ypres offensive began.

Sassoon declared: “I am making this statement as an act of wilful defiance of military authority, because I believe that the war is being deliberately prolonged by those who have the power to end it…

“I believe that this war, upon which I entered as a war of defence, has now become a war of aggression and conquest.”

Days later these words were read aloud in the House of Commons. Although Sassoon was to retreat into political silence (and even to return to the front), and although no prosecution followed, the thing had been said and heard.

Direct opposition to an imperialist war by anti-war socialist groups was being pursued in the context of increased working-class anger at ever higher food prices and related profiteering, while in manufacturing districts sharpening class tensions, expressed through the advance of the shop stewards’ movement and mass engineering strikes in May.

Anti-war fires in Britain were being stoked too as a consequence of the March revolution ending Tsarist rule in Russia, and bringing with it power-sharing with a provisional government by workers’ and soldiers’ councils — soviets.

If the importance of June’s Russia-inspired convention in Leeds of Workers’ and Soldiers’ Councils — supported widely by left-wing groups — can be exaggerated, the fact remains that such a gathering the previous year could not have been imagined.

It was in this changing environment that on August 10 a Labour Party conference voted by a large majority for a full international socialist conference on peace aims, and to include German socialists.

This was an unprecedented blow to the government’s war policy, supported as it had been by Labour leader and war cabinet member Arthur Henderson.

Lloyd George then forced Henderson’s resignation, but sadly the conference majority in favour of the conference barely survived a second vote on August 21.

The project was aborted but the level of support for it within the Labour Party and trade unions proved that the peace forces were gathering strength.

Such was the overall backdrop to the Passchendaele offensive, during which war fatigue was evident in the mutiny of thousands of British troops at the base camps of Etaples beginning on September 9.

There the most brutal of training regimes faced soldiers before consignment to the front, causing them to regard the Red Cap military police-run hell at Etaples as worse than the hell of the trenches.

The killing of an ordinary soldier by a Red Cap sparked the week-long mutiny, which featured hand-to-hand fighting and for a while was out of control. It has been estimated that 10 mutineers were shot after court martial. Some official records about the affair are still withheld from public access.

An enormously powerful hint that in time the war parties might be defeated by the peace parties came on November 7, three days before the end of the offensive, when the Russian Bolshevik Party, led by Lenin, assumed political power in Petrograd. The following day came its Peace Decree, of which four million copies were speedily sent to the eastern front. This called for an end to all hostilities.

Weeks later the Bolshevik government released the texts of the infamous secret treaties made between the Allies, and immediately the Manchester Guardian’s man in Petrograd, Michael Phillips Price (later a Labour MP) sent back dispatches about the treaties.

Full articles appeared in three issues of the paper before the end of November. Phillips Price commented much later in his memoir, My Three Revolutions, after listing agreements in which France and Romania were to be beneficiaries of territory: “Then there was the treaty giving Russia Constantinople and five […] provinces of eastern Turkey, while France got Syria and Great Britain Mesopotamia. There was another iniquitous treaty which, after the war, would virtually have partitioned Persia between Great Britain and Russia…”

Other national newspapers reported the “secret treaty” revelations scantily, but the Manchester Guardian had, for many people, nailed the lie that Britain’s role in the war was a disinterested one, that it had gone to war to defend “little Belgium.”

The truth was that the war, for Britain, was to maintain and if possible to extend its empire. For Germany it was to snatch part of the empires of Britain and France for itself. Sassoon’s declaration was not fantasy.

A year was to pass after the bloody Passchendaele fiasco, before the German revolution (following advances secured by massive reinforcement from US forces) finally ended the war.