A routine grenade exercise at a Canadian military base turned lethal when shifting winds drove flames into a training area, killing four soldiers and injuring 39 — and raising hard questions about the readiness of the ally America trusts to help guard this continent.

Canadian Brigadier-General Vanessa Hanrahan told reporters Thursday that the fire broke out October 17 on the automatic grenade launcher range at Canadian Forces Base Wainwright in Alberta during what she called "routine military training activities." The blaze started in the range's "Permanent Danger Area," which meant firefighters couldn't attack it directly and were forced to just monitor it for hours. Then the wind shifted. "A subsequent change in wind direction and velocity significantly increased the fire's intensity and rate of speed which led to these tragic events," Hanrahan said.

The toll: four soldiers dead and 39 injured, with 27 still hospitalized. The dead were identified as Sergeant Morgan Wong of Edmonton, Private Shaun Farrell of Prince Albert, Saskatchewan, Private Aidan Goulding of North Vancouver, and Private Hayden Lykkemark of Langley, British Columbia. They were members of Charlie Company, 3rd Battalion, Princess Patricia's Canadian Light Infantry, and Army reservists.

Here is the detail that should alarm every American taxpayer. Major-General Wade Rutland acknowledged Sunday that military officials knew about the fire for hours but believed it was contained, so they allowed training to continue before the winds suddenly shifted. About 84 soldiers were split between two training areas — one for grenades, one for practicing attacks on simulated enemy positions. The fire swept into the second area. Canadian Prime Minister Mark Carney said the blaze "jumped nearly a kilometer in less than a minute to where soldiers were gathered."

CBS News reported that Carney has brought in 50 investigators and promised answers "as expeditiously and transparently as necessary." Al Jazeera noted this was one of the worst peacetime tragedies for Canada's military.

What neither outlet pressed is the question that matters most to Americans. These soldiers were training for a deployment next spring to reinforce Canadian troops serving with NATO in Latvia — Canada's largest international military operation. CFB Wainwright regularly hosts NATO training exercises. The Canadian military is supposed to be a credible partner in continental defense through NORAD and a meaningful contributor to NATO's deterrent posture in Eastern Europe.

Instead, Ottawa's forces couldn't execute a live-fire exercise on their own prairie grasslands without losing four of their own and sending nearly three dozen to the hospital — in part because leadership let training continue around a fire they were only monitoring, not fighting.

Canada has chronically underfunded its military for decades. The bills for continental defense and European deterrence still get paid — just mostly by American taxpayers and American troops. This fire is a tragedy for those four soldiers and their families. It is also a symptom of a broader problem: a NATO ally that cannot safely run its own training ranges is an ally that cannot credibly share the load it has signed up to carry.