To date, two US Companies use Very Large Air Tankers: Global SuperTanker and 10 Tanker. At the request of the state of California in 2010, NASA* has analyzed this issue and published a report demonstrating the efficacy of using such devices in firefighting. However, these aircraft (DC10 and Boeing 747), are particularly suited to the geographical nature of the American terrain, as well as the strategic planning and policy of the United States (regarding army structure and local civil securities).
SuperTanker and 10 Tanker modules are exclusively dedicated to aerial frefighting missions. This weakens business model as there are not so many fires outside peak season. Thanks to the aircraft modularity, Kepplair Evolution profitability is independent of fires occurrences every year.
* USFS Very Large Aerial Tanker Operational Test and Evaluation
** Water taker aircraft operating base with specific infrastructure allowing water/retardant quick refill