On December 13, 1981, Jaruzelski began a crack-down on Solidarity, declaring martial law and creating a Military Council of National Salvation ("Wojskowa Rada Ocalenia Narodowego", or "WRON"). Solidarity's leaders, gathered at Gdańsk, were arrested and isolated in facilities guarded by the Security Service ("Służba Bezpieczeństwa" or "SB"), and some 5,000 Solidarity supporters were arrested in the middle of the night. Censorship was expanded, and military forces appeared on the streets. A couple of hundred strikes and occupations occurred, chiefly at the largest plants and at several Silesian coal mines, but were broken by ZOMO paramilitary riot police. One of the largest demonstrations, on December 16, 1981, took place at the Wujek Coal Mine, where government forces opened fire on demonstrators, killing 9 and seriously injuring 22. The next day, during protests at Gdańsk, government forces again fired at demonstrators, killing 1 and injuring 2. By December 28, 1981, strikes had ceased, and Solidarity appeared crippled. The last strike in the 1981 Poland, which ended on December 28, took place in the Piast Coal Mine in the Upper Silesian town of Bieruń. It was the longest underground strike in the history of Poland, lasting 14 days. Some 2000 miners began it on December 14, going 650 meters underground. Out of the initial 2000, half remained until the last day. Starving, they gave up after military authorities promised they would not be prosecuted. On October 8, 1982, Solidarity was banned.