Berkeley took a conspicuous part in the
First English Civil War, supporting the royal cause. He became governor of
Exeter, and general of the royalist forces in
Devon. In 1642 he joined the
Marquess of Hertford at
Sherborne, and was sent into Cornwall with the rank of commissary-general to act under
Sir Ralph Hopton as lieutenant-general. The royalist forces defeated, in May 1643, the Earl of Stamford at the
Battle of Stratton, with great loss of baggage and artillery, and pursued him as far as
Wells. In this affair, Sir John distinguished himself and was now made commander-in-chief of all the royalist forces in Devon. He sat down before Exeter, into which the Earl of Stamford had withdrawn, and which was further defended by the fleet under
Robert Rich, 2nd Earl of Warwick. Berkeley succeeded in maintaining a blockade, beating off the Earl of Warwick with a loss of three ships, and on 4 September 1643, the Earl of Stamford was compelled to surrender. In 1644, Berkeley was present at the baptism of
Henrietta Maria, the king's daughter, who was born at Exeter. The same year Hopton and Berkeley joined their forces to oppose
Sir William Waller's westward advance, but were badly beaten at the
Battle of Cheriton near
Alresford in
Hampshire on 29 March. In April 1645, he superseded
Sir Richard Grenville, being made colonel-general of the counties of Devon and Cornwall, took Wellington House, near
Taunton, by assault, and then proceeded to invest Taunton. The advance of
Thomas Fairfax westward in the autumn of the year changed the aspect of affairs. In January 1646 Fairfax was able to concentrate on Exeter, which Berkeley was forced (13 April) to surrender, on honourable terms. ==Involvement in the Hampton Court escape==