Originally Posted by
DodgyGeezer
If you can put a device with a low/undetectable radar signature over a foreign country then you have a useful means of first-strike attack.
The only problem I can see is that to avoid being visibly detected you would have to stay in cloud. And balloons navigate by varying their height so as to stay in a layer of wind moving in the direction they want to go, so they might have to move out of cloud occasionally. But this could be handled by waiting until the right meteorological conditions....
Hot air balloons can control their direction in a limited fashion by changing altitude but they still go directly downwind. Of course this makes them very observable in the IR!
Gas balloons can gain height by dropping ballast and lose height by venting gas but they still go downwind and there is a limit to how many times it can be done. Moreover, ballast is carried at the expense of payload.