[1] Sir Walter Erle, a local Member of Parliament with strong Calvinist views,[2] secured the ports of Weymouth, Lyme Regis and Wareham, along with Portland Castle, for the Parliamentarians during the build-up to the fighting.

[3] Dorset was a relatively inconsequential county of itself; it had no large cities, did not have significant industry, and though it had the aforementioned ports, none were major naval or trading bases.

By the end of 1643, most of the area was under Royalist control; only Plymouth, Poole and Lyme Regis held out against them,[6] but the Earl of Essex swept through the region in the summer of 1644, claiming most of Somerset and Devon for parliament.

His army suffered a heavy defeat at the Battle of Lostwithiel in September,[7] and scattered back into Dorset, leaving only Plymouth and Taunton as significant Parliamentarian controlled towns in Cornwall, Devon and Somerset.

[10] The regimental preacher, Peter Ince, said of the defences that "we were in as sweet a quiet and security as any garrison in the Kingdom; no enemy near us but one at Portland, and that not very considerable, being but about 300 or 400 men".

[14] The strength of the forts was such that despite their smaller numbers, the Royalists were able to hold them until the following day, when Dyve and the governor of Portland Castle, William Hastings, arrived with 1,500 men to clear out any resistance and garrison the town for the King.

[10] In order to retake Weymouth, Parliament dispatched the warship Constant Reformation under William Batten, with 200 sailors from Poole, and 100 cavalry under James Heane who had made their way through enemy lines and met up with Parliamentarians in Melcombe.