The Coup
The rebels divided their forces into three groups. First unit, with the coup leaders, took the Town Hall at Saxon Square, where they established their command center. As neither Dmowski nor Haller were in Poland (they were in France, attending the Treaty of Versailles negotiations), Sapieha and Januszajtis-Żegota declared that they were assuming the leadership of the country. They also sent a squad general Stanisław Szeptycki, and for the 21st Infantry Regiment, whose command supported the coup, to report to the Town Hall. Szeptycki however was first informed of the events by an officer who escaped from the Town Hall; then arrested by a rebel squad, and finally freed by his own soldiers. Investigating the matter, he arrived at the Town Hall, where he was in no mood for supporting the rebels: instead, as a ranking officer on the scene, he took command of the 21st Regiment and ordered the troops to siege the Town Hall. Hence, the coup leaders found themselves besieged by the very troops they intended to use to cement their victory.
The rebel unit tasked with arresting members of Moraczewski succeeded in arresting the ministers, although they failed to assassinate Minister of the Interior, Stanisław Thugutt.
The third group, tasked with arresting Piłsudski, tried to bluff their way into the Belweder Palace where Piłsudski had his office and living quarters. Once inside, they declared their intent to arrest Piłsudski - and promptly found themselves locked inside one of the rooms by staff loyal to Piłsudski.
Next day, members of Moraczewski's were freed, and most of the coup supporters surrendered to the government forces.
Read more about this topic: 1919 Polish Coup Attempt