"The only way to get to an air temple is on a flying bison, and I doubt the fire nation has any of those!" - Aang
The concept of fire nation "Air power" doesn't come up until Season 1, Episode 17 "The Northern Air Temple". This is the first creation of the war balloon, proving that it was not around during the initial air temple invasions 100 years prior. The war tanks with the grappling hooks are also implied to have been created later, as it is mentioned "I remember my dad tinkering with the counter-balancing system", by Teo. For the fire nation zeppelins, those are much larger and heavier than even the war balloons and might have come after that, considering the zeppelins don't show up until later in the series.
Now, at the time of Roku's…
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