OTTAWA – Prime Minister Justin Trudeau is marking the 100th anniversary of one of the bloodiest chapters in Canada's wartime history, the Battle of Passchendaele, with a low-key ceremony.

More than 500,000 people, including 15,000 Canadians, were killed or wounded at during the prolonged fight, as weeks of rain and shellfire churned the battlefield into a sea of mud.

The actual importance of the battle to the allied war effort has long been debated, with many historians describing it as a senseless waste that accomplished little.

But the Canadians do have the distinction of having delivered victory where others could not, with nine later receiving the Victoria Cross, the British Empire's highest award for bravery, for what their actions at Passchendaele.

Under grey skies at the National Military Cemetery in Ottawa today, Trudeau told a small group of military members, veterans and school children that the sacrifices from that battle are proof of reckless leadership at the highest levels.

But he also said it was a battle worth remembering because of the perseverance and commitment that Canadian soldiers demonstrated under near-impossible conditions.