[1][2] On 16 July 1643, Lord Willoughby captured Gainsborough for Parliament, only to be immediately besieged by the Royalists under Sir Charles Cavendish.

[2] Parliament sent a relieving force under Sir John Meldrum and Colonel Oliver Cromwell, which beat the Royalists at the Battle of Gainsborough on 28 July.

He had Boston and the Eastern Association apparently open in front of him, but faced the prospect of the still-intact army of Lord Fairfax behind him in Hull.

[3] The Parliamentary warships Lion (captained by Thomas Rainsborough) and Employment arrived to control the Humber Estuary and bring in supplies.

[1][3][6] On 22 September, Oliver Cromwell crossed the Humber from Lincolnshire with arms and ammunition for the defenders, and joined the Fairfaxes in the defence of the city.

Four days later, on 26 September, Sir Thomas Fairfax ferried his dragoons and cavalry back across the Humber to join the Eastern Association forces in Lincolnshire.

The defenders launched a counterattack two days later on 11 October, with 1,500 men comprising soldiers from the garrison, sailors from the warships and townspeople.

The Parliamentarians began their advance into Yorkshire that was to culminate with Newcastle being besieged in York and the consequent Battle of Marston Moor.