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 : Vizefeldwebel Oskar Hennrich was a German World War I flying ace credited with 20 aerial victories. 
Answer : World War I

A: In which war did Oskar Hennrich fought?
****
Q: Context : The Boeing KC-767 is a military aerial refueling and strategic transport aircraft developed from the Boeing 767-200ER. 
Answer : Boeing 767-200ER

A: The Boeing KC-767 is based upon what?
****
Q: Context : The Battle of Sahagún (21 December 1808) was a cavalry clash at Sahagún, Spain, in which the British 15th Light Dragoons (Hussars) defeated two regiments of French cavalry during the Corunna Campaign of the Peninsular War. 
Answer : 21 December 1808

A:
When did Battle of Sahagún occurr?
****