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The world’s first practical firebomber was a Stearman, a 1939 Boeing 75 that had been converted into a cropduster. In 1955 a California agriculture applicator, Willows Flying Service, cut a hole in the airplane’s belly fabric and fitted the chemicals hopper with a flapper hatch that opened when the pilot pulled a rope, releasing 170 gallons of water. That August, the Willows Stearman, flown by ag pilot Vance Nolta, dropped those 170 gallons onto a fire burning in Mendocino National Forest, and then repeated the feat several times. The biplane was “a big assist in knocking down hotspots,” said one forest ranger. Though a few test drops had been made on controlled grassfires, it was the first time that a real forest fire had been at least partially quenched by free-fall water dropped from the air.

“Free-fall” water is an important qualifier, for there had been attempts as early as the 1920s to put out fires with airplanes that were literally water bombers. They carried water in wooden kegs, cans, buckets, waxed-paper bags, balloons and other missiles, and they attacked fires with these projectiles. Not surprisingly, the bombs proved to be of greater danger to firefighters on the ground than they were to the fire itself.

In 1956 six U.S. Navy surplus biplane trainers much like the Stearman—Naval Aircraft Factory N3Ns—were also turned into firebombers, and Willows had itself a squadron of what the local newspapers called “aerial firewagons.” By the summer of 1957, the Willows fleet was ranging throughout California, answering calls from local fire departments as well as the California Depart­ment of Forestry and the U.S. Forest Service.

Willows Flying Service went on to become a pioneer air­tanker operator, but it soon became apparent that dropping just water on a raging fire wasn’t particularly helpful. The hotter the fire, the more water evaporated before reaching the ground. Adding sodium calcium borate to the water created a heavy slurry, a “fire retardant.” Though better compounds were soon developed, airtankers were for a long time lumbered with the generic handle “borate bombers.”

In the mid-1950s, everybody involved in California firefighting was aware of serious research into the potential for fighting fires from the air. Operation Firestop, a multi-agency brainstorming session, began in January 1954, after a particularly bad wildfire season in California left 140,000 acres charred and 14 firemen dead. One of the items on Operation Firestop’s agenda was discussion of techniques to drop water or firefighting chemicals from the air.

But first, there was a fortuitous event.

In the spring of 1953, Douglas was flying the DC-7 prototype out of Palm Springs Airport, east of Los Angeles, with a big water tank mounted as ballast in what would become the passenger cabin. At the end of flight-testing, the four-engine Doug made a low pass over the Palm Springs runway and dumped its ballast through three six-inch valves in the airplane’s belly. The result was a wide, mile-long swath of wetness that quickly caught the attention of the DC-7’s pilots as well as observers on the ground. So the LA County Fire Department and California Division of Forestry set brushfires on Rosamund Dry Lake and got Doug­las to take a run at them with the DC-7. The small valves released an ineffective mist, however, and the fires flared back up soon after the drop. Douglas increased each valve to 18 inches in diameter, and then demonstrated several times that a lot of free-fall water dumped all at once just might work.

Cal Forestry was particularly impressed, and with the help of the University of California’s School of Forestry set up some well-instrumented testing to quantify the effectiveness of this new way to fight wildfires. An Eastern Aircraft TBM-1C hired from Paul Mantz’s movieplane fleet flew the tests. Mantz built a plywood tank into the Avenger’s torpedo bay, which not surprisingly leaked like…well, a plywood sieve. So he switched to using a Weather Bureau balloon as a container for the slurry. That worked, leak-wise, and when the torpedo bay doors were toggled open, the rubberized balloon bulged out the hole before bursting and dumping the slurry. Ultimately, Mantz installed a metal tank in the TBM, and in 1958 it became the first of many Avengers to work real wildfires when it dropped slurry on a fire at Lake Elsinore. Mantz and his partner Frank Tallman became pioneer firefighting pilots, and increasing numbers of Avengers would become the first war surplus firefighting workhorses.

TBM Avengers were among the first warbirds converted to tankers for firefighting duties. (U.S. Forest Service)
TBM Avengers were among the first warbirds converted to tankers for firefighting duties. (U.S. Forest Service)

But before that happened, Operation Firestop testing began at the U.S. Marine Corps’ Camp Pendleton, north of San Diego, where thousands of acres were put at the disposal of the California firefighting researchers. Mantz flew his TBM over deep Pendleton canyons and made drops during different wind conditions. The canyons were laced with horizontal and vertical steel cables at various heights to hold anemometers and other test instrumentation. Each of the TBM’s dumps was analyzed for dispersal, wind drift, effectiveness and other criteria.

Operation Firestop, which ended in the fall of 1954, was responsible for aerial firefighting tools and techniques that, though they have evolved over decades, are still being used today. In the late 1950s, Consolidated PBY-5A amphibians followed the Avengers in the firefighting role, and they starred in Holly­wood’s take on the airtanker world, the 1989 film Always. The opening features a Catalina firebomber in one of the most memorable aviation movie intros ever shot. PBYs were slow, but they carried a substantial load, and their low-speed capability enhanced the accuracy of retardant drops.

PBYs pioneered the technique called scooping, in which a seaplane waterbomber rapidly force-fills its tanks while step-taxiing, thus obviating the need to land and refill from a ground supply. To be fair, in 1945 Canadian Noorduyn Norseman pilot Carl Crossley fitted his airplane with a pipe through which he could fill a tank with water after landing on a lake. Crossley made three successful drops on an Ontario fire, though the concept was then abandoned.

Today, even single-engine floatplane airtankers scoop to fill their pontoon tanks with water, and in the mid-1960s scooping led to the development of the world’s only purpose-built airtanker, the Canadair CL-215 amphibian, which first flew in 1967 and has since become the Bombardier CL-415 turboprop. The Russians and Japanese have both modified existing flying boats for firefighting duty, and the Chinese have flown a very large four-turboprop amphibian with a firefighting role, but the 215/415 remains the sole production waterbomber.

A Canadair CL-215—the world’s only purpose-built airtanker—swoops low over a wildfire in Provence, France. (STOCKFOLIO® / Alamy)
A Canadair CL-215—the world’s only purpose-built airtanker—swoops low over a wildfire in Provence, France. (STOCKFOLIO® / Alamy)

The most spectacular scoopers were the four enormous Martin JRM Mars flying boats bought in 1959 by a consortium of Canadian lumber companies. Fitted with 7,200-gallon tanks, the big boats sucked up a load in 25 seconds. Some scoopers were limited to dropping just water, but the Mars had room for large tanks of additives that could be added to the water in flight to create foam and gelled drops.

Within less than three years, one Mars had crashed, killing its crew of four, and another was destroyed during a typhoon. Only one, Hawaii Mars, remains flying, though in July 2016 owner Wayne Coulson put it up for sale due to high operating costs and lack of firefighting contracts.

Soon after PBYs appeared as airtankers, another Con­solidated Navy bird joined them: the PB4Y-2 Privateer, a single-tail patrol bomber derivative of the B-24. Priva­teers were declared surplus in 1954, and a number of them were snatched up by firebombing operators. So began the warbird years of airtanking, with many military surplus bombers, fighter-bombers and freighters converted to fight fires. Among the earliest were a number of B-17s, 10 Grumman F7F Tigercats, three North American AJ Savages—tubby piston twins with an auxiliary Allison J33 jet engine—and even a few Northrop P-61 Black Widows.

Sixteen B-25s were also operating in California by 1960, but that July four crashed within a few days. The remaining Mitchells were forever banned from firebombing in that state. Douglas A-26/B-26s, however, were more successful. During the mid-1960s, there were nearly 60 Invaders opera­ting in California alone, though by 1970 most were gone—scrapped, sent to Canada or bought for restoration
by warbirders.

After 20 years of service, the TBF/TBM tankers were at the end of their useful lives; many had crashed, and parts were becoming rare. In 1973 three more Avenger tankers crashed (plus three F7Fs in 1974), and the pressure was mounting to find a replacement. The answer: another Grumman, the stubby S-2 antisub twin typically known as the “Stoof,” for its original S-2F designation. By the mid-2000s, most firefighting Stoofs had been converted to turboprop S-2Ts.

Another warbird that joined the California firefighting fleet during the 1970s was the “Dollar Nineteen”—the Fairchild C-119 Flying Boxcar. Some were modified to carry a 3,400-pound-thrust Westinghouse J34 turbojet atop the fuselage, but a combination of structural problems and maintenance-heavy Pratt & Whitney R-4360 Corncob engines grounded the Fairchilds by 1987.

Though they aren’t airtankers, the small, maneuverable aircraft that carry air attack officers are an important part of the aerial firefighting fleet. Operating directly above the fire, AAOs control every move that airtankers make. They coordinate with ground firefighters, run multiple radio frequencies to control often-complex air traffic, keep an eye on wind and visibility, warn incoming tankers of specific ground hazards, mark the target with smoke and even lead airdrop runs. Sometimes the AAOs aren’t pilots, since they have enough to do without flying the airplane.

Air attack aircraft usually have been general aviation or ex-military small twins and even light jets, ranging over the years from Beech Barons and Cessna O-2s—military Sky­master push-pulls—to Commander turboprops and “Slowtations” (Ces­sna Citations). Today, North American Rockwell OV-10 Broncos have become the gold standard.

Airtankers are separated into four categories, depending on the volume of their slurry/water tanks. Smallest are the SEATs (single-engine air tankers), which are typically modified ag planes such as Grumman Ag-Cats, and light helicopters, all with tanks or “Bambi Bucket” slingloads of up to 599 gallons capacity.

Next up the spectrum are the Type III medium tankers, 600 to about 2,000 gallons: Grumman S-2s, CL-215/415s, Fokker F-27s and the like.

Type II includes everything that was at one time considered to be moderately large, carrying 1,800 to around 3,000 gallons per load: Lockheed S-2s and P2V Neptunes and a variety of other warbirds. Most of these airplanes are gone, mustered out by the mid-2000s through groundings, but a few are still working.

Type I firebombers are the big boys—3,000-plus gallons aboard Boeing KC-97s, Lockheed P-3 Orions and C-130s and converted jet airliners.

And now there is a subset of the Type Is: megatankers. King of that hill is the Global SuperTankers Boeing 747-400, which can transport almost 20,000 gallons at 520 knots and drop it at 140 knots, creating a swath of retardant three miles long and 100 yards wide. During August 2017, the 747 flew its first domestic sorties, against four California fires, dropping almost 250,000 gallons of retardant. The megatanker had previously flown against fires in Chile and Israel.

The only other U.S. megatankers are three converted DC-10s operated by the New Mexico firm 10 Tanker Air Carriers. The trijets have been active since 2006, and though their 11,600-gallon loads can’t match the 747’s tankage, it’s still the equivalent of almost a dozen drops from a Grumman S-2T. A modern Russian four-engine jet airtanker, the Ilyushin Il-76TD, can carry 11,000 gallons, but it has never been brought to the U.S. “We’re not having any Russians coming here and fighting our fires,” said one benighted FEMA executive.

Though its 3,000-gallon capacity hardly makes it mega, another effective new airtanker, the four-engine British Aerospace BAe 146/Avro RJ85 regional airliner, has been popular in Europe but until recently never made a major impact on the U.S. market. Eighteen are already at work out West, with more on the way.

While tankers get more and more mega, firefighting doctrine is increasingly favoring controlled, accurate, small drops from SEATs rather than the deluges unloaded by big firebombers. The biggest tankers are dangerously unmaneuverable at very low altitudes, and their considerable wingspans have led to higher drop altitudes, making the retardant less effective.

Coulson Flying Tankers’ Hawaii Mars makes a demonstration drop at EAA Airventure in 2016. The giant flying boat can scoop up 7,200 gallons of water in just 25 seconds. (Mike Collins/AOPA)
Coulson Flying Tankers’ Hawaii Mars makes a demonstration drop at EAA Airventure in 2016. The giant flying boat can scoop up 7,200 gallons of water in just 25 seconds. (Mike Collins/AOPA)

Many people don’t understand that airtankers do not “put out fires,” no matter how large they are. Like infantry doing what no air force can, firefighters on the ground beat down wildfires, albeit with the help of air drops. Aerial firefighting is of the greatest use while a fire is young. The tankers can try to contain a new fire with firebreak lines of retardant before ground firefighters can even reach the site. Dropping hundreds of thousands of gallons of retardant on a raging, well-established inferno, however, is about as effective as pissing on a bonfire.

Homeowners in the West have been building substantial homes on the edges of magnificent forests filled with tinder, much like people who insist on populating floodplains and barrier islands. This has led to the firefighting phenomenon known as the “CNN drop.” When a wildfire threatens such forestland houses—as was the case last October with the hellacious fires in northern California—those homeowners figure nothing is being done unless they see firebombers in action. They know from cable news that a big white airplane spewing a curtain of red retardant means the cavalry has arrived, so when a state senator demands that the fire boss order up a P2V to make an expensive but meaningless run, the firefighters call it a “CNN drop.”

Eventually, most of the warbird airtankers had become from 50 to 60 years old, corroding and inevitably overstressed. Flying firebombers is the most dangerous peacetime occupation an aviator can pick. By 2015, 38 American pilots and crewmembers had died during the preceding dozen years—five percent of the active pilots, proportionally the equivalent of 200 ground firefighters dying every year.

At the beginning of the 2000s, the U.S. Forest Service was committed to a lowest-bidder process for choosing the airtanker operators with which it contracted. This forced the companies selling such services to use the cheapest airplanes and helos they could haul out of a boneyard, and to cut corners on mainte-nance wherever possible.

In 2002 these practices nearly destroyed the large-airtanker industry. A C-130A crashed when its wings broke cleanly off, and two months later the same thing happened to an ancient PB4Y-2 Privateer operated by the same contractor, its wings collapsing downward. Most of us assume that when the wings come off an airplane, it has been overstressed with positive Gs—either somebody pulled too hard on the yoke or turbulence upset the airplane. But the wings of heavy airtankers can also fail under negative Gs. When an airplane suddenly drops 25 tons of retardant and leaps upward, a compromised spar can fail the wings downward.

The 2002 crashes, combined with a 1994 accident that had killed seven, led the National Interagency Fire Center to ground California’s large-airtanker fleet. That fleet declined from 44 aircraft to just nine that were cleared for further flight. What followed has been characterized as a “lost decade” for large tankers. The load was largely shifted to the shoulders of S-2 and S-2T (turbine) Tracker Type III medium airtankers. But in October 2014, all 22 of California’s S-2Ts were grounded when one crashed fatally while fighting a Yosemite National Park fire.

Today’s Western airtanker fleet is mainly made up of the surviving P2Vs, recently tankerized BAe 146s and Avro RJ85s, several other large aircraft, including two DC-10s, and lots of relatively modern single-engine SEATs and helicopters.

Standing by at eight locations across the United States are Air Force Reserve and Air National Guard MAFFS (Modular Airborne Fire Fighting System) C-130s. They are a court of last resort, only employed when every civilian resource is already in use. These Hercules airtankers discharge their load through two fat pipes that fire out of the opened loading ramp, the retardant forced out by 1,200 psi of compressed air. Some MAFFS Herks have large pintle valves protruding from special replacement units for the jump doors on either side of the aft fuselage. The system is a rapid-response, roll-on/roll-off rig; no airframe mods are needed.

Trouble is, the MAFFS C-130s are flown by military crews, and whether they are lifers or part-time airline and corporate pilots, they have little firefighting experience. They can only fly if they’re guided by skilled pilots in lead aircraft, and even then it’s a challenge. Tactics, radio work, air traffic control, coordination with the air-attack officer overseeing the entire operation—there’s more to it than simply pulling a dump-valve handle. In 2004 San Diego County tried to quick-train Navy and Marine helicopter pilots to be firefighters, but it proved to be impossible.

One relatively recent development is computerized dump valves that can be set to dispense retardant at different rates and amounts. In some cases, these valves can be controlled by GPS to drop on a precise, preset line. Predator UAVs were also recently used as camera and information-gathering platforms above the northern California wildfires, data-streaming to the ground incident command post. And the most optimistic of aerial firefighters look toward the day when airtankers will be designed from the ground up for firefighting, purpose-built for that one job—the perfect aircraft to wield as-yet unimagined weapons against fire.

Will that ever happen? Probably not. But there is no technology in existence—at least not at a reasonable cost—that will allow the continued use of the classic prop-driven heavy tankers. By the middle of the 21st century, U.S. wildfires are expected to double in acreage burned and intensity. As climate change creates warmer and drier conditions, severe wildfire years will probably occur two to four times per decade rather than the current rate of once every 10 years.

Whether part of the answer is the increasing use of megatankers or of swarms of SEATs and helicopters—the two currently opposing views of aerial firefighting strategy—firebombers aren’t going away.

At least nobody still calls them borate bombers.

Contributing editor Stephan Wilkinson suggests for further reading: Aerial Firefighting, by Wolfgang Jendsch; and Young Men and Fire, by Norman MacLean.

Firebombers! originally appeared in the March 2018 issue of Aviation History. Subscribe here!