The Evergreen 747 is a 747 converted to fire fighting.
It's main force is the ability to land fully loaded with water. Thus, it doesn't have to dump the water when it returns, having failed to find the fire. Obviously an important scenario.
It's weakness is exposed in the following quote: "provided refilling options and landing zones are available". What is the practical capacity of the thing, if it has to transit to a 747 capable airport to refill the water tank?