The US military on Tuesday ordered four air tankers to join fire-dousing efforts in Arizona, where firefighters were battling a still out-of-control inferno which killed 19 of their comrades, AFP reports.
The Modular Airborne Fire Fighting System (MAFFS) planes will be redeployed from other states to help tackle blazes including the Yarnell Hill fire, which remained zero percent contained despite a doubling of ground crews fighting it.
Investigators are still probing exactly what happened in Sunday's tragedy, the most deadly wildfire incident in 80 years and the biggest firefighter loss of life since the September 11, 2001 attacks in New York.
More tributes were added to a make-shift memorial outside the local fire station where the mostly-young firefighters, part of the Granite Mountain hotshots, an elite group sent in first to tackle blazes on the ground.
All but one member of the 20-strong team perished in the blaze, after a wall of flame they were trying to stop apparently blew straight into them. Some had sought refuge in last-ditch cocoon-like protection shelters, but to no avail.
The fire which killed them remains out of control. Over 400 firefighters are working on the blaze, up from 200 before the tragedy, after the area ravaged by flames quadrupled in size from 2,000 to more than 8,000 acres.
The extra firefighting aircraft, which are specially-equipped military C-130 planes, can drop 3,000 gallons of water or fire retardant in less than five seconds, and can be refilled in less than 12 minutes.
They are expected to all be in place by midday Wednesday (1900 GMT), said a statement by the US military's Air Expeditionary Group for wildfire fighting, based in Boise, Idaho.
Four additional MAFFS-capable C-130s are operated by Air National Guard units in North Carolina and Wyoming and can be called on if needed, it added in a statement.
The Yarnell Hill blaze was the most lethal since 340 firefighters died in the ashes of the Twin Towers in New York on 9/11, and the most deadly wildfire since 29 died fighting a blaze in Los Angeles's Griffith Park in 1933.