RAF balloon command was based in Kent as I remember though there were balloons around most major cities, particularly south of London though. As for your grandfather, as a motorcyclist the chances are he was a dispatch rider and so you will need to find out what regiment he was with so that you can work out which theatre, campaigns, operations and actions he was involved in (in that order). If you have any of his documents or personal effects from the time they should yield some interesting information (I founf my grandfathers ID card from when he was on embarkation leave to be sent to the far east, twice he was trained, kitted out and sent on leave but each time he was called back to his unit for one thing or another). That would save you some money and probably be more interesting (and more helpful as the records office can be rather obstructive at times).

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There's no honorable way to kill, no gentle way to destroy. There is nothing good in war. Except its ending.