The 747 Supertanker

The Supertanker was a Boeing 747 converted into the largest aerial firefighting aircraft ever flown — an aeroplane that could lay a line of retardant several kilometres long in one pass.

How it worked

Conventional air tankers use gravity: doors open, the load falls out. The Supertanker used a pressurised delivery system instead, pushing retardant out through nozzles under pressure.

That mattered for two reasons. It let the crew control the flow rate, so a single load could be split into several separate drops or laid down at different intensities. And because the liquid was expelled rather than dropped, the aircraft could release from a higher altitude — safer over mountainous terrain, where low-level tanker flying is among the most dangerous work in aviation.

The aircraft

The first conversion, by Evergreen International Aviation, was based on a 747-200 and rated at up to 24,000 US gallons (94,850 litres). It was certified by the FAA and flew on fires in the United States and abroad.

After Evergreen ceased trading in 2013, the concept passed to Global SuperTanker Services, which converted a 747-400 named Spirit of John Muir. Certified in 2016, it fought fires in California, Chile, Israel and Bolivia, and became the aircraft most people picture when the Supertanker is mentioned.

The argument about whether it was worth it

The Supertanker was never uncontroversial. Supporters pointed to the sheer volume — one aircraft delivering what would take a fleet of smaller tankers many sorties.

Critics argued that wildfire suppression rarely rewards volume alone. Very large aircraft need long runways and specialised reloading facilities, which are seldom close to a fire; they cannot work the tight, low, terrain-following patterns smaller tankers fly; and dispatching one is expensive whether or not it changes the outcome.

Retirement

The end came for commercial reasons rather than operational ones. Global SuperTanker Services announced in May 2021 that it was ceasing operations, citing insurance and maintenance costs compounded by pandemic disruption to charter contracts. The aircraft was retired that October, sold to National Airlines, and converted back into a freighter.