One of those aircraft is the Boeing 747-100 Supertanker operated by Evergreen International. According to information provided by the company:
The multi-role B747 Supertanker is the largest tanker aircraft available today. With a payload of more than 20,000 gallons and a response time of 600 mph, it has more than eight times the drop capability and twice the speed of any other federal air tanker currently fighting fires. The Supertanker’s patented pressurized system has the capability to disperse product at high pressure for an overwhelming response, or disperse at the speed of falling rain in a single or several segmented drops. This pressurized system will also allow for drops at higher altitudes, creating a significant safety buffer and enabling the Supertanker to fight fires during the day and at night, when they are most vulnerable.The video below shows some demonstration flights of Evergreen International's B747-100 Supertanker.
If the video does not play or display properly above, click here to view it on YouTube.
For more detailed information about both the B-747 and DC-10 tanker aircraft and their use in aerial fire suppression, see USFS Very Large Aerial Tanker Operational Test and Evaluation, a 24-page report ('pdf' file).