All Blacks coach Steve Hansen says you learn more from defeats than victories. That is probably as true of war as it of sport.

It sometimes seems we remember only wartime defeats, particularly those in the Great War of 1914-1918.

The centenary of its memorable battles brings them back to life more vividly than they have ever been to generations born in or since World War II.

The name Passchendaele has been inscribed in New Zealand's memory as a term for terrible, unspeakable slaughter.

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And it was.

One hundred years ago today, the New Zealand Division of the 2nd Anzac Corps took its turn to attack the German line just beyond the town of Ypres in Belgium where British commanders hoped for a breakthrough after three years of trench warfare on the Western Front.

The division's objective that day was Bellevue Spur near the village of Passchendaele, behind the German line.

It was raining heavily, as it had been for most of the week since the New Zealanders had taken part in the successful battle of Broodseinde not far away.

New Zealanders were involved in victories in the Great War and some of them are well remembered, such as at Messines that summer.

That was a battle that encouraged the high command to believe they could break through at the Ypres salient and cut off Belgium's channel ports, bases for U-boats that were taking a heavy toll of merchant ships supplying Britain.

But in the days leading up to October 12, designated for the advance on Bellevue Spur, the rain did not let up.

The low ground in front of the spur became a quagmire and, crucially, the division's artillery could not be properly positioned.

Artillery barrages had to precede infantry advances in order to remove the advantages of defenders dug in with machine gun posts and barbed wire.

In the mud and slush the heavy guns could not accurately blast away the concrete bunkers and shred the wire.

That was predictable. The division's commander, Major General Andrew Russell, and others, urged a delay for a break in the weather but the Corp commander, General Alexander Godley, and Army commander Field Marshal Douglas Haig, were determined to attack that day.

At dawn the order was given. The soldiers went forward as best they could, wading in mud under machine-gun fire.

Any who made it as far as the barbed wire were doomed to die on it. Within hours, New Zealand had suffered its largest death toll in a single day. The division was virtually destroyed.

A month later Canadian troops succeeded where the New Zealanders had failed. The Canadian commanders insisted on proper preparation for the battle and favourable weather.

As at Gallipoli, the New Zealanders at Ypres had cause to rue their deference to British generals.

Australia and New Zealand emerged from the Great War with more faith in their own practical judgement and determined to keep more autonomy of command in future wars.

Today our foreign policies and defence arrangements are adhering to the lessons learned in the shock and sickening horror of Passchendaele's bloody mud.