After defeating Essex at Lostwithiel in September 1644, the main Royalist army from Oxford under Charles I arrived outside Plymouth, and demanded its surrender. Since Parliament still controlled the sea, they were able to provide supplies and reinforcements, including a regiment led by the experienced and aggressive Colonel John Birch. This allowed the garrison to refuse terms and with the Royalist army urgently needed elsewhere, Charles left only a minor force under Sir Richard Grenville to continue the blockade.