Detailed Instructions: Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.
Q: Context : The 21st Army Tank Brigade was an armoured brigade formation of the British Army active during World War II. The brigade served with the British First Army and the British Eighth Army during the fighting in Tunisia and Italy.
Answer : British Army
A:
Who did 21st Army Tank Brigade serve for?