(CNN) - Arizona firefighters battling a deadly blaze are getting big help from the U.S. military: four specially equipped C-130 firefighting aircraft, CNN has learned from the Defense Department.
The planes will help fire crews attack the zero-contained Yarnell Hill blaze.
Extreme heat, strong winds and parched land from drought are hindering efforts to stop the wildfire, which has scorched more than 8,400 acres -- about 13 square miles of land.
Nineteen firefighters from Prescott died Sunday in the wildfire, a loss called "unbearable" by Gov. Jan Brewer. About 400 ground personnel and 100 incident management staff are working to control the raging fire around 80 miles northwest of Phoenix.
The C-130 crews will have their work cut out for them in battling what is now considered the deadliest fire in state history.
Equipped with the Modular Airborne Fire Fighting System, or MAFFS, the planes, loaded with water or fire retardant, can drop 3,000 gallons in less than five seconds. The retardant covers an area one-quarter of a mile long and 60 feet wide.
They can return to base, reload and be airborne again in under 20 minutes.
The planes are from Colorado, where crews had been working on fires for the last several days. But they are now considered more vital for Arizona. The military deployment is coming at the request of civilian firefighting authorities asking for additional support.
A Defense Department official confirmed the details to CNN but declined to be identified because an announcement has not yet been made.
Late Monday afternoon, the Yavapai County Sheriff's Office advised residents in the communities of Peeples Valley and Yarnell to evacuate their dwellings. An estimated 200 homes and other structures burned in Yarnell.