On the morning of the 7th August 1642, to the "considerable agitation and suspense [of the] town", a naval squadron of seventeen ships appeared in Galway Bay. Led by Alexander, 11th Lord Forbes (died 1671), they had come to relieve the garrison of Forthill1 at the request of the English Parliament, and which had authorised him, as Lieutenant-General, to waste the coasts of Ireland. Launching long boats from the ship, Forthill was resupplied with food, arms and ammunition. Forbes then sent a messenger with a letter for Mayor Walter Lynch fitz James, ordering them to "confess themselves to have been rebels, and humbly submitting to beg his majesty's intercession for them to the parliament of England, and to declare they would admit such governors as the king and state should appoint, and until then put themselves under the protection of Lord Forbes."
Mayor Lynch and the town council utterly refused the terms, to the surprise and anger of Lord Forbes. They instead made representations to the Earl of Clanricarde - who was at the time a neutral - for protection. Clanricarde in turn communicated to Forbes that, should he make war against the town, it would be both a breach of the peace and endanger the country by bringing yet another area into the war. Furthermore, he made it clear that, should the citizens become actively hostile against Forbes, there would be nothing he could do to influence them.
According to James Hardiman " ... Forbes, stimulated by Willoughby and Ashley" - captains of the besieged Forthill - "and governed by the advice of Hugh Peters, whom he brought with him as his chaplain ... was entirely deaf to every remonstrance of reason or discretion." Being unable to directly assault the town itself, Forbes landed men west of the town and took possession of the Claddagh2, on the west bank of the Corrib. All of the town's surrounding suburbs and villages were burned and destroyed; dozens of locals were killed, assaulted and raped. St. Mary's Church in the Claddagh was badly defaced; in its graveyard, coffins were dug up as Lord Forbes's troops searched the bodies for rings, gold chains and the like.
Forbes placed "two pieces of ordnance", or cannons, at St. Mary's and used them to bombard the city. However, they had little effect and by early September Forbes's men were becoming irritated at both their lack of progress and lack of payment. On the 7th September he cut his losses and sailed for Limerick. Forthill was once more under siege and on its own, Clanricarde's political stock had plummeted as he had being unable to prevent the sacking, and any waverers among the people of Galway were now solidly on the Irish Confederate side.

