The song is about the breaking of the seige of Derry. "Walker's zeal, and Murray's steel Came in their need to cheer them, And sallies from open gate, Soon taught their foe to fear them" The Defenders held the city until relieved by "Browning's vessel"
OrangeLark: "'No Surrender' is a phrase often used in Ulster. The song traces its origin to the Seige of Derry and names a few of the city's defenders who have been memorialized in Apprentice Boys Clubs." The chorus is "Then raise the cheer, to freemen dear, And toast each brave defender; For nought imparts to Derry hearts A thrill like 'No Surrender!'"
See Historical References to "The Boyne Water" for a summary of the war in Ireland between James II and William of Orange. [Or see the detailed duscussions under "The Shutting of the Gates of Derry" and "The Battle of the Boyne (I)." - RBW]
The Protestant Plantation of Ulster was created after the 1607 "Flight of the Earls" -- heads of the Ulster clans -- to Rome allowed James I to declare their lands forfeit to the Crown. In the Plantation, the City of Londonderry was fortified and gated walls built around it. When James II brought troops from Ireland [to England,] Londonderry was left unguarded. On December 7, 1688, Lord Antrim's Catholic "Redshanks" camped outside the city. With the city government undecided as to how to handle the situation, thirteen young "Apprentice Boys" seized the gate keys, drew up the drawbridge and locked the four gates. Antrim's troops withdrew. Lord Mountjoy's Protestant regiment was allowed to garrison the city. To escape the war, residents surrounding areas flooded into the city. Reinforcements sent by William to relieve Derry in April turned away. Then James's attempt at negotiating with Derry failed. Colonel Murray led Protestant troops to the gate, which was opened for them, and the Derry government, which had been willing to negotiate with James, was overturned. Reverend George Walker and Colonel Henry Baker were appointed joint Governors. The seige began "in earnest" on May 5, 1689. On July 28 three ships on the Foyle broke the seige bringing food; captain of the Mountjoy was Michael Browning, who was killed in the battle. The beseigers left on August 1, 1689. (source: Cecil Kilpatrick, "The Seige of Derry: A City of Refuge" at the Canada-Ulster Heritage site) - BS