The "band of brothers" is a reference to the speech of Henry V to the outnumbered English forces before the battle of Agincourt on St Crispin's day:

Crispin Crispian shall ne’er go by,

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.

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More Info: en.wikipedia.org