On the outbreak of the Second World War, Zuckerman left Warsaw for the
part of eastern Poland that had been occupied by the Soviet Union. He
remained there, organizing branches of the underground, until he was
ordered to return to German-occupied Poland in April 1940 in order to
perform a similar task. Using the code-name "Antek", he helped to
found and edit the underground press, promote the political ideals of
the movement, and establish the Dror high school. He made
surreptitious trips to many other ghettos, once spending a month
travelling throughout the Generalgouvernement visiting cities and
towns, such as Lublin, Zamosc, Hrubieszow and Kielce, where he
continued to promote the establishment and organization of the
movement's branches and cells. Everywhere he encountered the same
picture - degradation, depression, helplessness.

On 24 April 1941, whilst he attended a meeting of a Zionist collective
in the Warsaw Ghetto, the Germans arrested Zuckerman together with 100
other activists. They were transported to a camp in the Kampinos
forest to dig canals and drain swamps. In his evidence at the trial of
Adolf Eichmann, Zuckerman described conditions in the camp:

"I think up to ten people died daily, together with those who were
shot because they were suspected of being about to escape… I
encountered death from starvation there for the first time. People
were talking amongst themselves and suddenly one of them, without any
warning, would die. And I was thinking all the time how I was going to
die. But I was younger, possibly also stronger, and I did not die of
starvation."
After a few days in the camp, a courier was sent to seek out
Zuckerman. She was Lonka Pozhivieska (Kozibrodska), a Jewish girl who
had been deported from Pruszkow to Warsaw. She was posing as a
non-Jewish Polish girl, but she quickly aroused the suspicion of the
guards. Zuckerman continued:

"I was taken away for interrogation… they wanted to know whether she
was a Jewess or not. Since I knew that she did not have the badge,
that she had come without it, I argued all the time that she was a
non-Jewess; we had studied together at school and obviously she had
got to know about [my arrest] and had come [to see me]. Afterwards
they accused me of `Rassenschande' (Race Defilement), because she was
not Jewish. They said they were going to execute me."
Zuckerman was not executed. Instead he was placed in a pit full of
water:

"Towards morning I was taken out in front of the whole camp, and the
camp commandant announced roughly the following words: `This man knows
when he was born, but he does not know when he will die.' And he
promised that for three days and three nights my body would be
suspended from the gallows. I stood there and waited for death. But I
was taken back to the pit…"
Zuckerman was released from the pit, and eventually, after payment of
a sufficiently large bribe, from the camp itself. He returned to
Warsaw and began to organize a resistance movement.

As reports reached Warsaw in the autumn of 1941 of the activities of
the Einsatzgruppen in the Soviet Union, many Jews reached the
conclusion that educational activities were no longer of any value.
Instead, it was necessary to plan for armed Jewish resistance. The
resolve of Zuckerman that this was the only course of action left open
was strengthened when a messenger bearing horrific news arrived in
Warsaw in November 1941. His name was Heniek Grabowski. Masquerading
as a non-Jew, he had been sent from Warsaw to Vilna by the Jewish
community. Now he returned to describe the murder of thousands of the
Jews of Vilna at Ponary. Zuckerman was devastated; in his own words,
now it was known "that the disaster is total. I am from Vilna myself.
I was born in Vilna. I left all of my parents and relatives behind in
Vilna. And here he brought this tragic news from Vilna. While still a
child, I had played among the trees of Ponary, and here he spoke about
Ponary. My Vilna, the Jews of Vilna, were being killed in Ponary, my
playground."

Another bearer of sickening tidings arrived in Warsaw on 19 January
1942. A young Jew from the village of Izbica Kujawska, Ya'akov
Grojanowski, escaped from the Chelmno death camp Sonderkommando. After
he had eventually reached Warsaw, he provided detailed testimony
regarding the camp. The 28 March 1942 issue of the underground
newspaper Jutrznia ("Dawn") carried the following article:

"… We know that Hitler's system of murder, slaughter, and plunder
relentlessly leads to a dead end and the destruction of Jewry. The
fate of the Jews in the areas of the Soviet Union conquered by the
Germans and in Warthegau signifies a new phase in the complete
annihilation of the Jewish population. The gigantic killing apparatus
has turned against masses of weak, unarmed, hunger-stricken Jews in
the form of camps and deportations… There can be no doubt that Hitler
… intends to drown the Jews in a sea of blood. Jewish youth must
prepare itself for such difficult days. Mobilization of the vitality
of the Jews will therefore begin. Many such vital forces still exist,
despite the destruction. From generation to generation, we are
troubled by the burden of passivity and lack of faith in our own
strength; but our history also contains glorious and shining pages of
heroism and struggle. We are obliged to join those eras of heroism…"
Zuckerman was among those who attempted, without success, to form a
unified military resistance movement from among the various Jewish
underground groups. In spring 1942, Zuckerman joined the short-lived
Anti-Fascist Bloc, a largely Communist inspired attempt to amalgamate
five different Jewish factions in order to carry out military
operations, only for this organization to also rapidly disintegrate.
Zuckerman commented:

"On the one side, in the East, it burned and it burned on the other
side from the West. Chelmno was in the Warthegau. We were in the
middle. Could we think that the fire would not come upon us? In what
way were we any better, we the Jews of Warsaw, the Jews of the
Generalgouvernement, that they should treat us differently? These were
arguments we put forward concerning ourselves and concerning others,
concerning the Jewish community."
When the deportation of Jews from Warsaw to Treblinka began on 22 July
1942, an emergency meeting was held in the ghetto by a group of
prominent Jews. On behalf of He-Haluts, Zuckerman proposed that the
seizure of Jews be resisted by force, a demand that the meeting
rejected. On 28 July, Zuckerman attended another meeting, this time
consisting only of the leaders of the youth movements Ha-Shomer
ha-Tsa'ir, Dror and Akiva, where it was decided to form the ZOB
(Zydowska Organizacja Bojowa – Jewish Fighting Organization).
Zuckerman was appointed a member of the group's new headquarters,
along with Shmuel Breslaw, Josef Kaplan, and Zivia Lubetkin (who was
to become his wife). Leaflets were published, stating: "Aussiedlung
(Resettlement) means Treblinka, and Treblinka means death"; Jews were
called upon to hide. In the final days of the Aktion, members of
Ha-Shomer ha-Tsa'ir and Dror met to discuss the grievous events of the
past weeks and what the future held for them, as Zuckerman recalled:

"… The words were bitter; words of decision. Jewish resistance will
never come into being again after us. The nation is lost. The masses
did not place their trust in us. We do not have – and probably never
will have – weapons… But this tiny group might yet save us. Let us go
out into the streets tomorrow, set the ghetto aflame, and attack the
Germans with knives. We will die. It is our duty to die. And the
honour of Israel will be saved…
… Despair was the dominant feeling, and that feeling demanded action…
The discussion was heated, the atmosphere torrid. But gradually more
tempered voices began to be heard. Concrete suggestions were raised.
It was a fateful night for the remnants of the Jewish Fighting
Organization. We took a vote and resolved to pluck up our courage and
rebuild the armed Jewish force. Our remaining strength would be
dedicated to that end. No effort would be spared. The fate of January
and April 1943 was sealed on that night."

Disaster struck the ZOB on 3 September 1942. Breslaw and Kaplan were
arrested and executed. Zuckerman and the remaining leaders decided to
transfer their pitifully small cache of weapons – five pistols and
eight hand grenades - to a new hiding place, but the person
transporting the arms, Reginka Justman, was stopped by a sentry. The
weapons were seized and Justman shot. Completely demoralized, some
members of the ZOB proposed attacking the Germans with their bare
hands, but Zuckerman, Lubetkin, and Arieh Wilner convinced them to
rebuild the shattered force. The leaders proposed that after the
Grosse Aktion there would be a lull in the deportations, which would
enable the ZOB to obtain further arms and plan an uprising.

In December 1942, the ZOB sent Zuckerman to Krakow, where he
participated in an attack by the Jewish underground on the Ziganera
Café, an establishment patronized by German officers. In a subsequent
incident in Krakow, Zuckerman was badly wounded in the leg and only
managed to make his way back to Warsaw with great difficulty. There he
was appointed commander of the eight groups of Jewish fighters in the
area of the Toebbens-Schultz workshops, one of the three areas into
which the underground had divided the ghetto.

On 18 January 1943, the poet Yitzhak Katzenelson paid a visit to
Zuckerman's unit and was about to return to his home. After a short
while Katzenelson returned, telling Zuckerman that everything was
lost, that the walls were surrounded, that massive detachments of
Germans were besieging the ghetto and had actually penetrated it. The
Germans surprised Mordechai Anilewicz' unit, who were captured by the
Germans and marched in the direction of the Umschlagplatz, together
with a large collection of other Jews. Upon a signal given by
Anilewicz, the members of his unit, who were amongst the ranks of the
arrested, attacked the Germans and threw a hand grenade. At first
there was great panic. The Germans scattered, and so did the Jews.
Zuckerman's group witnessed the entire incident, although they were
too far away to participate. They realized from this incident that
they could not afford to be drawn into street fighting. Instead, they
would adopt partisan tactics and fight in the houses. Zuckerman
testified:

"We in our group - those of us whom they didn't manage to capture -
fought in the houses throughout two days. The position was such that
the group was small, about 40 persons, and only some of them were
armed - we were easily able to circulate amongst the houses, on the
roofs. And it seemed to the Germans that several groups were
operating; in fact they were small units. We obtained arms, we also
killed Germans, we also took their arms from them, we obtained both
hand grenades and rifles, this was important to us. And the last thing
that we received - the faith that we knew how to fight."
Amazingly, after four day's fighting the German's withdrew. On the
last of those four days, the Nazis shot 1,000 Jews in the ghetto
streets, apparently an act of pique because the ghetto was no longer
silent and submissive.

In April 1943, Zuckerman was ordered to cross over to the "Aryan" side
of Warsaw, to act as the ZOB's liaison officer with the Polish
underground. He remained on the "Aryan" side for six days without any
money or documents. On the morning of 19 April, he arranged for a
messenger, Frania Beatus, a girl aged 17, to go to the wall of the
ghetto in order to contact a Jewish policeman, a member of the
underground, and ask him to pass on the message that Zuckerman was
about to join up with a work party that was returning to the ghetto.
But at seven a.m. she returned, crying bitterly, and said: "All is
lost." It was too late – the ghetto had been surrounded. On that same
day, the Warsaw Ghetto Uprising began. Beatus said she was going to
commit suicide rather than be captured. She kept to her word on 12
May.

Isolated on the "Aryan" side, Zuckerman desperately tried to obtain
and supply arms to the fighters in the ghetto. He made contact with
members of the Armia Krajowa (Home Army; AK) and the Communist Gwardia
Ludowa (People's Guard; subsequently renamed the Armia Ludowa,
People's Army; AL), the principal Polish underground military
organizations, but apart from receiving a few rifles from the Gwardia
Ludowa, met with little success. In the final days of the uprising,
after many failed attempts, Zuckerman was one of the team that
arranged for some of the remaining ghetto fighters to be extricated
via the Warsaw sewers. Later, Zuckerman was to explain the anguished
policy of the ZOB:

"… I am almost positive that we could have gotten many more fighters
out of the ghetto. But we were afraid to leave so much as a crack open
for retreat. Our fear was that we might arouse the notion that a man
could save his life even if he did not fight. It was for that reason
alone that we did not prepare any `safe houses' on the `Aryan' side,
or cars or people who could serve as guides through the sewers… Our
hour had come without any sign of hope or rescue."
Zuckerman wrote to Mordechai Anielewicz and to Zivia Lubetkin in the
ghetto. He received a very formal, polite reply from Anielewicz and a
very aggressive response from Lubetkin, who complained: "You haven't
done a thing so far. Nothing.". Anielewicz' letter included the
following:

"23 April 1943. Shalom Yitzhak. I don't know what to write to you.
I'll waive personal details this time. I have only one expression to
convey my feelings and those of my comrades. Something has occurred
which is beyond our wildest dreams. Twice the Germans fled from the
ghetto. One of our squads held out for 40 minutes, and the second -
for more than six hours. The mine which had been buried in the brush
makers' area exploded. On our side only one victim has so far fallen:
Yehiel, he fell as a heroic soldier beside his machine gun.
"When the news reached us yesterday, that members of the P.P.R.
attacked the Germans and that the Schweitz radio station broadcast the
wonderful news about our self-defence, I had a feeling of
completeness. Although we still have much work to do, everything that
has been done so far was done to perfection.

"The general situation: All the workshops in the ghetto and outside it
were closed, except for "Werterfassung," "Transavia" and "Dering."
Regarding the situation with Schultz and Toebbens, I have no
information. Communications have been cut off. The workshop of the
brush makers has been in flames for three days. I have no contacts
with the units. There are many fires in the ghetto. Yesterday the
hospital was burning. Whole blocks of buildings are in flames. The
police has been disbanded, except the "Werterfassung." Schmerling
surfaced and has reappeared. Lichtenbaum has been released from the
Umschlag. Not many people have been taken out of the ghetto. This is
not the case with the "Shops." I don't have details.

By day we sit in our hideouts. From evening we change to the partisan
method of activity. Three of our units go out at night - with two
objectives: armed patrols and obtaining arms. You should know - a
revolver is of no value, we have hardly made use of it. What we need
are: grenades, rifles, machine guns and explosives. I cannot describe
to you the conditions under which Jews are living. Only a few chosen
ones will hold out. All the others will perish sooner or later.

Our fate has been sealed. In all the bunkers where our comrades are
hiding, it is impossible to light a candle at night for lack of
air...of all our units in the ghetto only one man is missing: Yehiel.
Even this is a victory. I don't know what else I should write to you.
I can imagine to myself that you have one question after another, but
this time please let this suffice. Be well, my friend, perhaps we
shall meet again. The main thing: the dream of my life has been
fulfilled. I was privileged to see Jewish self-defence in the ghetto
in all its greatness and magnificence. Mordechai."

With the final suppression of the uprising, Zuckerman remained in
"Aryan" Warsaw, and together with others who had managed to escape,
became active in the movement known as the Jewish National Committee
(Zydowski Komitet Narodowy; ZKN). This movement provided assistance to
Jews who were in hiding, as well as maintaining contact with Jews
incarcerated in certain of the labour camps, or fighting with the
partisans. In March 1944, Zuckerman compiled a comprehensive report on
the establishment and achievements of the ZOB, which was forwarded to
London by the Polish underground. Zuckerman was also among those who
continued to appeal via this channel for the rescue of the little that
remained of what was once called "The Jewish Nation in Poland." At
first news items were passed on by the secret radio station that was
at the disposal of the AK; later, reports were transmitted by means of
airplanes which came to collect the communications of the Polish
underground.
On 1 August 1944, the second, National Uprising commenced in Warsaw.
About 1,000 Jews, at least 50% of whom were subsequently killed, were
divided into three groups and took part in the fighting. Commanding
the second group, made up of surviving members of the ZOB, was Yitzhak
Zuckerman. Still active, the ZKN published leaflets, one of which,
issued on 22 August 1944 under the title A Voice from the Depths",
contained the following:

"And so, Hitler has not attained his objective. And he shall not be
able to attain it. The Jewish people lives! Out of 17 million, over 5
million have been exterminated. But the Jewish people of 12 million
fights with greater determination and force for its existence and for
its better future. The Jewish masses throughout the world share our
tragedy with us; they suffer together with us, and are doing all they
can to arouse the whole world concerning our situation and coming to
our help. They are fighting with great energy and enthusiasm in order
to re-establish Jewish life anew and to bring about an economic and
social resurrection.
Only one, sole historic compensation can be considered after the flood
of Jewish blood that has been spilled: an independent, democratic
Jewish State in which the tortured Jewish people will have an
unrestricted opportunity for development and productive existence."

Those Jews who had survived, including Zuckerman and his wife, Zivia
Lubetkin, now sought shelter in the countryside or went into hiding in
Warsaw. In November 1944, a Polish doctor, Stanislaw Switala, offered
a refuge in his hospital to seven former leaders of the ZOB, including
Zuckerman and Lubetkin. The long nightmare finally ended in January
1945 when the few Jewish survivors of Warsaw were liberated by the
Soviets. Zuckerman now devoted himself to relief work, participating
in the revival of the He-Haluts movement and the exodus of Jews from
Poland to Palestine in 1946 and 1947 known as the Beriha.
Zuckerman and his wife themselves left for Palestine in early 1947,
where they were among the founders of Kibbutz Lohamei ha-Getta'ot (the
Ghetto Fighters' Kibbutz) and Bet Lohamei ha-Getta'ot (the Ghetto
Fighters' Museum), one of the most important institutions of Shoah
commemoration and research. Zuckerman devoted the remainder of his
life to these causes until his death in Israel in 1981. He made a
brief appearance in Claude Lanzmann's film Shoah, saying bitterly: "I
began drinking after the war. It was very difficult… If you could lick
my heart, it would poison you."