I stumbled upon this thread looking for the same information and then I found the answer, so I thought I’d post it here:
Basically, they were were put in a brand new jail and they would do things like bend the frames so the doors couldn’t close. In the song Utah is recounting a story told to him, so it was probably not clear about the banging and how they broke the jail, but it’s not that far off the mark. It also seems like it conflates three different stories (both from the same site):
“The I.W.W.'s cleaned the place from top to bottom and finally gained food demands, blankets, etc., by “battleship” methods-literally hammering the jail apart. Committees of women were allowed to bring cooked food to the prisoners in Seattle and later in Everett. I was at one of the “banquets” served on tables set the full length of the jail corridor-a full meal topped off with cigars and flowers.”
"The ones charged with murder were moved to the brand new and escape-proof Snohomish county jail in Everett. What they fed us there looked like the swig a farmer throws to his hogs. We had to build another battleship. We threw the stew on those fine new wails, and we were able to force the cell doors open. We couldn’t do anything with the tank doors, but we bent the cell frames so they could not be latched properly.
The fellows downstairs took all the levers from the upper locking system and bent them out of shape. That cost $980 to repair. I told McCullough, the man who had since been elected sheriff, that he could have bought a lot of good food for what that battleship had cost him."
"At Everett the 74 indicted men were held incommunicado for two months, denied any reading materials, and subjected to the mercies of Sheriff McRae and his deputies. Revolted by the vile food, the prisoners went on a hunger strike, and won. Denied blankets and mattresses and forced to sleep on the cold steel floor in the chill November nights, the prisoners “built a battleship.” With buckets and tins and such bits of metal as could be wrenched loose, they beat upon the walls, ceilings, and floors of the steel “tanks.”
Others linked themselves arm in arm and jumped in unison, shaking the walls of the jail. All the while they shouted at the top of their lungs. So great was the din that townspeople gathered around the jail, thinking that the deputies perhaps were murdering the inmates. The prisoners won their blankets.
On Thanksgiving Day a committee of Everett people, helped by members of the Cooks and Waiters Union, cooked a special dinner for the prisoners; Sheriff McRae turned them axvay and ordered a holiday feast of mush. At one time a different type of “battleship” was built to protest the bad food. The cell doors were pulled open by blankets tied to them.
With small pieces of pipe the mechanism of the locking system above the doors was broken and then the entire system of locks demolished. Outside their cells the men had access to some 300 pounds of corned beef that had been piled in a corner."