To battle the more than 50 wildfires now burning across the western United States—including the massive Rim Fire threatening Yosemite National Park in California—thousands of firefighters have employed a vast arsenal of technology, including hundreds of specialized vehicles.

The effort around the Yosemite wildfire, which has burned more than 284,000 acres and had been just 20 percent contained by Wednesday, has involved 16 helicopters, 49 bulldozers, 454 fire engines, and 39 water tenders, wheeled tankers that transport water.

The 4,000 firefighters battling the Yosemite fire and their fleets of vehicles resemble a small army in more ways than one: many of the tools and techniques firefighters in Yosemite and beyond are using can be traced back to just after World War II,