On first blush, of course, it would seem a real stretch. And you only need to think for a second or two about the kinds of thermals such large conflagrations create, in very large sections of air column above them, to know it would be a serious challenge to staying in the air at all, much less resist the kinds of structural loading that attempting such a thing would undoubtedly put such a craft through.

So right now it would be hard to say with any certainty. One thing I do know, though, that not nearly enough imaginative effort has been put into any kind of an alternative to what state emergency responders have in their current inventory to put great amounts of fire retardant (whether water or otherwise) were it is needed quickly. And of course as well, it always comes back to the money, or more precisely, the lack of it to do development work on much larger scale ways to go about such important delivery systems.

That being said, I would still like to think that, if any lighter than air approach was going to have any chance, one that borrowed from the principle of the pontoon bridge might have a pretty good shot at it; especially if the trains were fairly large, both in respect to the size of the individual train units, but also in the over all, connected length of the train. What this might boil down to is simply the fact of: can you engineer the linkage between the trains to be of sufficient strength to handle the sudden shifts of one, or more units, suddenly being thrust up, or down, against the current altitude of the remaining units still not in the same thermal event, or combinations of thermal events down the entire length of the train, going in all sorts of different directions. I'd also like to think that, whatever the engineering challenges, a way could be figured out to resolve them. But that is always the way it is with a dreamer.

Seeing as such trains would already have an immense possible impact on other critical transportation needs, and that we could set up refining the design as part of the public works project to create them in the first place, how much more trouble would there be in looking into this application as well? It might give us a new tool to really put massive amounts of retardant were we need it, and if nothing else it might spark a better imaginative approach, and with something just as unconventional.