On April 19, 1943, the Germans entered the Warsaw ghetto. The insurgents, mostly young people from the Jewish Fighting Organization and the Jewish Military Union, opened fire. The creator of the Underground Archive of the Warsaw Ghetto, Emanuel Ringelblum, witnessed the preparations and fights.
After the great deportation action in summer 1942, two military organizations were established in the Warsaw ghetto – the Jewish Combat Organization (JCO), established by members of left-wing parties, representing Zionists, communists and Bundists, and the Jewish Military Union (JMU), a right-wing organization, smaller but much better armed. Although both unions did not create a joint command, they agreed on the division of sectors for defense.
Zamenhofa Street between Wołyńska Street and Miła Street, looking north: Zamenhofa 29 (fragment on the left), Zamenhofa 31 and Zamenhofa 33 / Miła 31/ Stroop Report
Members of the Oneg Shabbat group who survived the previous liquidation actions in the summer of 1942 and January 1943 were involved in helping the JCO. Emanuel Ringelblum, Szmuel Winter, Icchak Giterman, Menachem Mendel Kohn, Aleksander Landau and others joined a committee that raised money for the Organization.
Warsaw Ghetto burning / JHI collection
A few days before the action, I visited the JCO combat post – wrote Ringelblum. – It was a two-room apartment with a kitchen at 32 Świętojerska Street, three floors below was a station of the German Werkschutz [factory guard]. There were 10 people in the place day and night, determined to give their lives if it was necessary. They were armed. The fighters were not allowed to leave the premises, they received food on the spot. To enter the premises, one had to go through the attics of the neighboring houses, and knock on the door in a pre-arranged way. The three female fighters present in the apartment prepared meals and carried out various dangerous missions and JCO orders. Discipline and order were exemplary. This group, under the influence of Poale Sion-Left [socialist Zionist party], carried out a number of successful expropriation actions (the so-called ‘exes’) for the purpose of arming the ghetto, etc. 
The JCO, the illegal ghetto government, was making vigorous preparations for defense. Terror was used to gain significant financial resources from war moneymakers, who would not voluntarily donate a zloty. The reluctant ones or their families were arrested in broad daylight and kept in secret apartments until a tribute was paid, amounting to dozens, and sometimes hundreds of thousands of zlotys. War was declared against the spies, Gestapo agents, traitors who assisted the Germans in the field of production (…).
Before the outbreak of the Uprising, Ringelblum also visited the JMU headquarters:
At the same time, I also saw the JMU arsenal of weapons. The headquarters were located in an uninhabited house at 7 Muranowska Street, in a 6-room apartment on the second floor. There was a first-class radio in the management room, bringing news from all over the world, and a typewriter next to it. The JMU leaders, with whom I spoke for several hours, were armed with revolvers tucked under their belts. In large halls, various types of weapons were hung on hangers, i.e. machine guns, rifles, revolvers of all kinds, hand grenades, ammunition bags, German uniforms – all of these equipment was intensively exploited during the April operation. There was a great bustle in the command room, as in a real army headquarters, orders were received for prepared “points” where future fighters were gathered and trained. Reports were coming about expropriations of wealthy people, who had to give money for the armament of JMU.
During my presence, they bought a guns for quarter of a million zlotys, for which an advance of 50,000 zlotys was given, from a former Polish officer. Two machine guns were purchased for 40,000 zlotys each, and a larger number of hand grenades and bombs. When I asked why the place was not secret, I was told that there was no fear of being betrayed by my own partisans, and if an unwanted stranger, e.g. a gendarme, would arrive there, he would not come out alive. 
To the left: Mordechaj Anielewicz, leader of the JCO. Drawing by Abba Fenichel / JHI collection
In April and May 1943, several hundred inhabitants of the ghetto put up armed resistance to the Germans. The report of Jürgen Stroop, the commander of the German forces, gives the number of 56,065 people murdered on the spot or captured and transported to labor camps or Treblinka.
Fate of the Oneg Shabbat group
Among the members of the Oneg Shabbat group, Izrael Lichtensztajn, his wife Gela Seksztajn and their daughter Margolit probably died during the first days of the uprising. Eliasz Gutkowski with his wife and son also died from the gas discharged into the sewers as they tried to escape from the ghetto. Menachem Mendel Kohn, the secretary of the group, who repeatedly saved his friends from oppression, was also killed. On May 3, the Germans discovered the bunker in which, among others, Szmuel Winter was hiding – they forced the residents outside with tear gas, and then escorted them to be shot. Eliezer Lipe Bloch, a social activist and friend of Ringelblum, was captured by the Germans and sent to a labor camp in Budzyń near Lublin, and then to other labor camps – he died in 1944 in Mauthausen.
Aleksander Landau with his wife and son left the ghetto. Hersz Wasser was captured by the Germans and sent to the labor camp in Trawniki, but he escaped from the transport and hid with his wife in Warsaw. Earlier, Emanuel Ringelblum with his wife and son had reached the “Aryan” side. However, just before the outbreak of the Uprising, Ringelblum returned to the ghetto. “The outbreak of the uprising on April 19 found Ringelblum in Brauer’s szop [forced labor workshop] at 32 Nalewki Street, where he may have gone to talk to Menachem Kohn who was employed there. Trapped in the burning ghetto, he could not return to Jehudis and Uri,” writes Samuel D. Kassow. Ringelblum was captured by the Germans and sent to a labor camp in Trawniki near Lublin, from where he was released in August by Teodor Pajewski and Róża (Szoszana) Kossower with the help of Adolf Berman.
Members of the Oneg Shabbat group: from top left – Izrael Lichtensztajn and Gela Seksztajn (Ruth Lahav collection), Eliasz Gutkowski, Eliezer Lipe Bloch, Hersz Wasser, Szmuel Winter.
Warsaw Ghetto burning / JHI collection
On April 19, Ringelblum saw the flags – white and red and white and blue – hung by JMU soldiers at Muranowski Square:
From the fifth floor of 32 Nalewki Street, I was an eyewitness to such a fight at Muranowska Street on Monday, April 19, in the afternoon. The trophies in the form of these banners were displayed by the Germans with pride at the Order Service Headquarters and they prided themselves on winning them. The fighters fired on the passing SS and Ukrainian units (e.g. from the house at 76 Leszno Street, where K.G. Schultz’s szop was located). Germans and haidamakas [Ukrainians] were shot at with revolvers and machine guns, hand grenades and bombs were thrown at the enemy. 
April action broke out. During the Sunday night (April 17-18), JCO patrols moved around the ghetto streets, urging people to hide in shelters. A hopeless fight has begun. The 6,000-strong German troops, armed with modern and motorized weapons, appeared on the streets of the ghetto. A handful of doomed, armed with revolvers of not the best kind, stood against this modern army; a handful of the best, noblest youth, aware of the doom that awaited them. 
They did not think how to survive the war, they did not possess Aryan documents, they had no apartments on the other side. Their only concern was to think about the most dignified, honorable death possible, as befits an old nation with a history spanning several thousand years.