the only 747 supertanker has been on the valley Fire in San Diego. 06 Sep 2020 Pictured: the only 1 747 supertanker and the largest in the world has been on the valley fire in San Diego. It carries up to 19,600 gallons of retardant. Photo credit: Ryan Grothe / MEGA TheMegaAgency.com +1 888 505 6342