John de Vere, 13th Earl of Oxford, was Henry's principal military commander. He was adept in the arts of war. At the Battle of Barnet, he commanded the Lancastrian right wing and routed the division opposing him. However, as a result of confusion over identities, Oxford's group came under friendly fire from the Lancastrian main force and retreated from the field. The earl fled abroad and continued his fight against the Yorkists, raiding shipping and eventually capturing the island fort of St Michael's Mount in 1473. He surrendered after receiving no aid or reinforcement, but in 1484 escaped from prison and joined Henry's court in France, bringing along his erstwhile gaoler Sir James Blount. Oxford's presence raised morale in Henry's camp and troubled Richard III.
