Ed Ballard

Consuming a few hundred acres, the fire in the Hürtgen Forest, western Germany, was a mere barbecue compared with the conflagrations that have recently threatened Mediterranean tourist spots and burned swaths of Canadian forest.

But the fire forced the evacuation of nearly 2,000 people from a nearby village. Extinguishing it took almost as many firefighters and other emergency personnel, as well as 10 helicopters.

The landscape presented its own challenge: It is littered with ammunition, the legacy of a World War II battle in which the invading U.S. First Army suffered more than 30,000 casualties. The unexploded ordnance, some of which was heard going off during the dayslong effort to quench the fire, made it harder for firefighters to get close to the blaze.

Explosive wildfires are another entry in Europe's fast-lengthening catalog of weather-related disruption. A scorching summer has shrunk rivers, parched crops and tested the continent's infrastructure.

High-tech responses are emerging. Last year, the state of Brandenburg bought two remote-controlled tanks-one with a grabbing arm and a fire hose that can shoot water or foam 180 feet, another that flays the ground to remove vegetation-and an armored vehicle for their operators to sit in. In the heavily forested state, where large areas served as training grounds in the former East Germany, nearly 20% of the land is suspected to harbor old munitions.

The system, which cost roughly $3.5 million, was deployed in late July and early August at a forest fire near a former military training area near the town of Jüterbog, said Norman Barth, a wildfire expert working for Brandenburg's government.

The idea is to let firefighters reach areas that hadn't been checked by bomb-disposal teams so they can cut firebreaks and douse strategic patches of land to protect key areas.

For Lindon Pronto, a Californian firefighter turned wildfire adviser who helped conceive Brandenburg's setup, the growing risk from unexploded ordnance is just one example of how fiercer blazes are straining firefighting practices in many parts of the world.

"It's changing everywhere," he said. "The intensity is catching people off guard."

Pronto envisions unmanned tanks aiding firefighters in other former battlegrounds such as Syria and-eventually-Ukraine, part of an array of devices aiding firefighting in hazardous terrain.

Others thinking along similar lines include Drone Amplified, a startup whose unmanned aerial vehicles drop balls containing fire-starting chemicals to ignite controlled burns. South San Francisco-based Burnbot has developed monstrous tracked machines with arrays of torches for the same purpose.

If these strategies take off, one ironic outcome might be a new business line for arms manufacturers.

Rheinmetall, the standard-bearer for European remilitarization, recently acquired a majority stake in DOK-ING, the company behind Brandenburg's remote-controlled vehicles (slogan: "Don't send a man to do a machine's job"). Rheinmetall has been making ammo since before World War I, and presumably its factories produced their fair share of the shells still lurking in Germany's soil.

In acreage terms, Germany's wildfires are small, but they are getting worse-and the conflicts of the last century add an extra dimension of peril. Johann Goldammer, head of the Global Fire Monitoring Center, a research and advisory group in Germany, said extended hot dry spells and the deterioration of old ammunition are making explosions more likely. The cyclical freezing and thawing of soil also brings old shells to the surface, Goldammer said, much as flower beds can seem to produce fresh stones every winter.

In the long run, containing Germany's wildfires may require deeper change. Barth said replacing flammable pine forests with mixed woodlands would help. So would accelerating the process of detecting and removing old munitions.

"Maybe we will be ready in 100 years," Barth said.

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Today's email was written by Ed Ballard in London. Contact him at ed.ballard@wsj.com. Contact the team at climate@wsj.com.