On his father's death, John inherited the by-now hereditary Mowbray office of Earl Marshal, and in August 1436 he accompanied the Duke of Gloucester.on campaign to France, specifically to raise the siege of Calais.
On his father's death, John inherited the by-now hereditary Mowbray office of Earl Marshal, although not all of his inheritance. In August 1436 he accompanied the Duke of Gloucester.on campaign to France, specifically to raise the siege of Calais.