[1] As Master Gunner of Artillery in the armies of Charles VII, Bureau acquired a reputation as an effective artillery officer during the Normandy campaign (1449–1450), when his bombardments helped capture the towns of Rouen, Harfleur, and Honfleur, and aided in the French victory at Formigny.

[3] Described as a "perfectionist with a methodical, mathematical mind" and "an imaginative technician who knew how to get the best out of his primitive weapons", Bureau likely learned the artillery trade for its commercial potential.

[3] The Bureau brothers were aided by innovations in the manufacture of gunpowder in the late 1420s that generated a more potent powder that could fire projectiles at a much greater velocity and did not require mixing in the field.

Cavalry reinforcements arrived later in the day to seal a decisive victory for the French, which paved the way for the capture of the remaining English strongholds in Normandy.

[1] In 1451, the Bureaus joined the French invasion of Gascony, in southwestern France, and were instrumental in the recapture of several cities, including Bordeaux, which surrendered in June.

Jean Bureau was appointed Mayor of Bordeaux in August 1451, but the local Gascon population revolted against the new leaders and invited the English to return.

Bureau, confident in the positions of his batteries, told the king, "I promise you on my life that in a few days I shall have demolished the town.

"[8] Hearing this statement, the delegation agreed to accept Charles' harsh terms, and control of the town was turned over to the French on 19 October 1453.