[nickparker]

Buoyant forces in the Martian atmosphere would be teeny tiny no? I don’t think blimps would work very well.

You could maybe get some sort of inflatable lifting body to work at high speeds though.

[TremendousJudge]

An advantage you have is that you can fill them with hydrogen and be fine, since there's no oxygen to allow them to suddenly combust

[mjevans]

Which you would then do what with, as there's no free supply of oxygen to burn it with in the engine?

[bashinator]

You would use the hydrogen in gaseous form to reduce the net weight of the aircraft to be lighter than the surrounding atmosphere (hydrogen gas has an extremely low density). This enables the craft to float without having to burn fuel just to stay aloft.

https://en.wikipedia.org/wiki/Airship