It's slang, reference to a 1930s American radio show called Gang Busters that started each episode off with excitement and action.
So it refers to something going well at first and being exciting from the start.
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"From this day to the ending of the world,
But we in it shall be remember’d;
We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother..."
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