This week, 40 years ago, was perhaps the most dramatic and nerve-wracking in the history of the state. It was the last , and the most difficult, of the three weeks that have become engraved in national memory as "the waiting period" on the eve of the 1967 Six-Day War. Most of the Egyptian army was already deployed in the Sinai, some of it in attack formation, while the Syrians were deployed on the Golan Heights. On May 28, Israel decided to wait for another "two or three" weeks. Two days later King Hussein of Jordan signed a defense pact with Egypt, thereby effectively subordinating Jordan and its army to the Egyptians.

Anyone who wasn't yet born then cannot possibly fathom the depth of the anxiety that gripped Israel. It was but two decades after the end of World War II, one generation after the Holocaust, and many of Israel's citizens, who were still of an age to engage in military action, were themselves survivors. This was a tiny Israel, located inside the 1949 armistice borders, which foreign minister Abba Eban called "Auschwitz borders."

Israel's nuclear project was borne out of the tremendous fear of another Holocaust, which was a guiding light for the project's father, David Ben-Gurion, and that week in May may have been its most dramatic.

Many of those involved saw themselves as partners in the making of a unique history. They were convinced that their activity signified a historic moment, and no politician, not even the prime minister, would be able to turn back the clock.

Many of the recently published studies of the Six-Day War hinted at the fact that the Israeli nuclear dimension played an important but hidden role in the events leading up to the war, but none of the books has focused on this aspect. Layers of ambiguity, secrecy and taboo, in addition to censorship, prevented the story from coming to light.

In my book "Israel and the Bomb" (1999), I tried to examine the crucial place of the Six-Day War in Israel's nuclear history. On the basis of commentary in Israeli and foreign publications, as well as additional documentary material, I suggested that it was on the eve of the war that Israel realized its nuclear option. Here, I will update that research. It should be noted that in the absence of official, authorized Israeli material, all of the assessments and conclusions made here are mine alone.

According to all the estimates, Israel had almost completed the research and development stage of its nuclear plan during the year that preceded the Six-Day War. The main partners in the plan's development had acted separately from each other both organizationally and technologically, but now they were approaching the point of convergence. To oversee coordination of their work, halfway through 1966, the Atomic Energy Commission was reconstituted as an administration responsible for dealing with nuclear activity, under the management baton of Professor Israel Dostrovsky of the Weizmann Institute. Prime minister Levi Eshkol decided that he himself would chair the committee and hold the ministerial responsibility for its sensitive work.

Despite the establishment of the commission, the political establishment still found it difficult to provide clear answers to the dilemmas that multiplied during the period preceding the Six-Day War. For the initial five nuclear countries (the United States, the Soviet Union, Britain, France and China), a successful nuclear test marked the transition from the infrastructure and R&D stage to the stage of building force and strategy. While such a test revealed the capabilities, it also publicly symbolized that the country had a nuclear political commitment. A test meant lifting the ambiguity surrounding the country's intentions.

According to expert opinion, from a technological perspective, Israel could have followed this procedure in full during the second half of 1966. At that point, Israel could have joined the Nuclear Non-Proliferation Treaty (NPT) as a nuclear country in every respect.

Delicate political consensus

But Israel was different. As I wrote in "Israel and the Bomb," as far as Eshkol was concerned, such a step was not a possibility. "What do you think, that the world will congratulate us for our achievements?" Eshkol would sarcastically demand of those who brought up the subject. And he had good reasons for thinking this way.

Eshkol knew that the act of revelation would be a gross violation of the commitment he had made to the American administration that Israel would not be the first country to introduce nuclear weapons into the Middle East. Ben-Gurion had used this formula back in 1962, and afterward Shimon Peres used it as well, at an improvised meeting with president John F. Kennedy at the White House in April 1963.

But the memorandum of understanding Eshkol signed in March 1965 with White House representative Robert Kommer turned this formula into an official Israeli commitment. Its precise meaning was vague, and Israel refrained from clarifying it. Eshkol, who fell in love with the formulation for exactly that reason, would, with a half-smile, ask the native English speakers around him (Abba Eban and Ya'akov Herzog) what exactly he was promising not to do in saying this.

Everyone understood that a revelatory act would signify a gross violation of the Israeli commitment. Beyond that, Eshkol knew that the great powers were in an advanced stage of discussing an international nuclear nonproliferation pact. An Israeli revelatory act would therefore be tantamount to a challenge to those powers, which would result in a diplomatic catastrophe in the relations with the United States on which he had worked so hard.

Furthermore, this commitment also had political significance inside Israel. The policy expressed a delicate internal Israeli consensus that the leaders of Ahdut Ha'avodah, one of the predecessors of Labor, especially Yisrael Galili and Yigal Allon, saw as a part of the sensitive coalition agreements still in place with Ben-Gurion. As far as they were concerned, this formula reflected a strategic Israeli interest and was no mere convenient and vague formulation. They believed that Israel had to develop a nuclear "capability," but not proceed beyond this stage and nuclearize the Middle East. It is hard to know what Eshkol thought about this view, but most probably, if only for political reasons, he was closer to Galili and Allon than to the Rafi (an offshoot of the Mapai party) people, Peres and Moshe Dayan, who at that time supported nuclear deterrence.

And of course there was the Egyptian factor. Eshkol knew very well that a revelatory act would be tantamount to a provocation that would ignite a regional war, as Nasser had indeed threatened in 1966, when he announced that Israel's deployment of nuclear weapons would require the launching of a preventive war.

Due to these special circumstances, the nuclear dilemma Israel began to grapple with on the eve of the Six-Day War was anything but simple. Israel had to decide what it wanted to do with its nuclear project: whether it wanted to develop nuclear weapons, or to develope a limited, virtual capability, and then rely on security guarantees from the United States, or even make peace with the Arabs. To put it another way: Israel had to decide on the real parameters of its nuclear plans, both with respect to infrastructure and with respect to products.

Israel's political leadership in 1966-1967 had difficulties providing clear-cut answers to those questions. Eshkol's difficulty derived in part from the fact that Ben-Gurion, the founding father of the nuclear project, had determined that big strategic questions should be set aside and the focus should be on the here and now. As I understand it, Ben-Gurion did not have clear answers, apparently not even for himself, as to where Israel should be heading after the completion of the research and development stage. A lot depended on the way the world would react to Israel's behavior.

It was only natural that the heads of the nuclear project would push for technological determination. They wanted to forge ahead even without a revelatory act. As far as they were concerned, freezing the project at the crucial point would amount to a betrayal of their work. The ethos of the project, as it was nurtured, was that a nuclear option meant usable capability for an existential (and unexpected) "moment of last resort." To the best of my understanding, as they saw it, Israel had to have a real nuclear option, not something amorphous.

A strike on Dimona

But it appears that prime minister Eshkol and part of the military top brass saw things differently during the months that led up to the Six-Day War. In my estimation, Eshkol's heart was more on the side of caution than toughness. I use a cautious formulation to express Eshkol's position on the nuclear issue for two reasons. For one, unfortunately, no public archival material exists that casts light on Eshkol's thoughts. The second and no less important reason is that the "meagerness of the material" has a real objective dimension: The nuclear ambiguity was convenient for everyone, including those like Eshkol, who did not want to decide, or found it difficult to do so. Nevertheless, it appears that now there are many testimonies, some of them better known and some of them less so, that indicate Eshkol's caution.

In his book "Eshkol, Give the Order!" (2004), Ami Gluska, using IDF documents from the highest level, revealed the concern among the top brass and the political level during the two preceding years about an Egyptian military response to Israeli nuclearization. The top military and government echelons assessed that the nuclear compound in Dimona was a major target for an Egyptian surprise attack, especially if and when Egypt believed Israel was close to producing a nuclear weapon. Worries such as this became central as Israel progressed in its nuclear activity.

Thus, Gluska describes how, at a meeting of the General Staff, toward the end of 1965, chief of staff Yitzhak Rabin said: "If the Egyptians bomb Dimona and we want to go to war, we will get an ultimatum from the entire world." Even though Egypt's military involvement in Yemen had, in the assessment of Military Intelligence, reduced the chances of an all-out war with Egypt, at the beginning of 1966 the heads of Military Intelligence perceived a pinpoint Egyptian attack on Dimona as not only possible, but likely.

Several months later, in October 1966, Rabin used Dimona in his arguments on why the IDF should practice restraint in the face of Syrian provocations. "There is an object in the south of the country that is an ideal object for a limited response [on the part of Egypt] and it would enjoy total support from the entire world for this. Dimona. [Government ministers] say [that] Egypt can't move troops [to Sinai or to Syria], but dealing with Dimona, that doesn't count as war. It would be a limited action." Gluska notes that the fear with respect to Dimona was translated into an explicit demand by the political level not to ratchet up the activity against Syria, as the army was demanding.

There are other indications with respect to the disquiet Dimona caused. During the year and a half before the Six-Day War, Mossad head Meir Amit invested great effort in examining the possibility of a profound change in Israeli-Egyptian relations, including even an opportunity for peace. Looking at the documents of this project, known as Icarus, which were published by Ronen Bergman and Tom Segev, and reading Amit's book "Head to Head," illustrates that Dimona looked to him like a possible diplomatic lever for a breakthrough with Egypt.

Amit was not the only one who thought this. MK Zalman Abramov of the General Zionists and a member of the Committee to Prevent the Nuclearization of the Middle East, tried to promote similar diplomatic ideas. When I interviewed him at the beginning of the 1990s, he spoke about his perception back then that it was possible and necessary to trade the Israeli nuclear option for the possibility of peace. He wrote personal memoranda dealing with this matter to Eshkol and Eban, and met with them, but it was unclear to him whether either ever did anything about it.

Further evidence for Eshkol's disquiet comes from another direction. In December 1966, there was a serious industrial accident at the Dimona compound. One worker was killed, a sensitive work area was contaminated and it took many weeks to purify and seal off the damaged area. The accident shocked all those responsible for the nuclear project, including the prime minister himself.

Recently published American diplomatic documents show how the U.S. ambassador to Israel at the time, Walworth Barbour, saw matters. In a letter Barbour sent in February 1967 to a senior person in the State Department's Near East Division, he wrote that he did not recall any other occasion when Eshkol had sounded so uncertain as to the future of Dimona. Barbour recommended to his correspondent that perhaps, from Washington's perspective, this was the time to move the idea of developing a large energy project, involving nuclear desalinization of water in Israel, into practice. According to Barbour, in return, Israel would place Dimona under inspection. In his letter Barbour writes that even six months earlier he had been certain that the Israelis would never be persuaded to give up their option of a nuclear weapon in return for the desalinization project, but he believed a number of new elements had entered the picture of late. He went on to say that one could sense a slackening of the determination to leave Nasser unwitting as to Israel's nuclear intentions and that the Israelis' awareness of the dangers inherent in this mode of action had become clear to him in a number of recent conversations with the prime and foreign ministers. He also wrote that his personal impression was that Dimona was not working at full-steam and that the most promising arrangement available on the horizon was the possibility that Israel would open Dimona to a significant number of non-Israeli scientists for inspection. He added that Abba Eban was thinking along those lines, which was significant, and that at least one trial balloon had been sent up recently in that direction.

Another piece of indirect evidence shedding light on Eshkol's hesitations arose in an interview I conducted with Floyd Culler, who headed the American team visiting Dimona in the late 1960s. Culler also headed the team that visited Dimona in April 1967, the last visit before the war broke out. During this visit the team was officially accompanied by Professor Amos de-Shalit, the scientific director of the Weizmann Institute.

On the last day of the visit, after a reception at de-Shalit's home in Rehovot, the host insisted on personally taking Culler back to his hotel in Tel Aviv. In the conversation between the two, de-Shalit brought up a number of suggestions Culler later described as the detailed thoughts of a physicist on how to prevent a nuclear Middle East. Although de-Shalit described his suggestions as "personal thoughts," Culler was convinced that the suggestions were a "trial balloon" launched on Eshkol's behalf, and he transmitted them to Washington as such.

From the little Culler was prepared to say on the subject, it was obvious to me that de-Shalit had made it very clear to him that now was the time to act in order to prevent a nuclear Middle East. Unfortunately, added Culler, within weeks the crisis in the Middle East erupted, and the nuclear issue lost its relevance overnight. Even decades later, Culler still related to the conversation with great delicacy, and he refused to go into detail.

Crossing the threshold

We are coming to May 1967. The standard Israeli narrative until now has never discussed the war's nuclear dimension. The memoirs of Eshkol's military secretary, Colonel Yisrael Lior, which were edited by Eitan Haber in the book "Today War Will Break Out" (1988), for the first time revealed the aerial photographs taken by parties hostile to Israel over "strategic targets" during the waiting period, and discussed the impact these flights had on the way Israeli politicians perceived the crisis. In two reports in the early 1990s in Haaretz, Aluf Benn was, I believe, the first to say that the Six-Day War also had a nuclear dimension, citing the somewhat opaque remarks of the founder of Rafael (Armaments Development Authority), Munia Mardor, about that "fateful weapons system my people have succeeded in bringing to operational readiness."

From Gluska, we learned how two high-altitude aerial photography flights over Dimona, on May 17 and 26, were critical for the IDF and the government's understanding of the Egyptians' intentions. On both occasions the atmosphere of crisis was exacerbated within minutes of the flights being discovered. The second flight was discovered in real time during a government meeting. Rabin and Eshkol went out for an immediate consultation. Rabin reported on "a strange and worrying transmission that reported about coordination between bombers and fighter planes." For a moment there was a fear that this was the start of an aerial attack on Dimona.

Eventually minister Moshe Carmel spoke of the "shock" that gripped the members of the government when they received the report of a "wing of fighter planes over the reactor in Dimona." In their new book, "Foxbats Over Dimona: The Soviets' Nuclear Gamble in the Six-Day War," Isabella Ginor and Gideon Remez for the first time suggest that the planes were not in fact MiG 21s, as stated in Israeli sources, but rather MiG 25s, flown by Soviet pilots.

However, at the same time, an even more important drama in the chapter of Israel's nuclear history was playing out somewhere else in the country. In my books "Israel and the Bomb" and "The Last Taboo," I have argued that the weapons system Mardor (with some injustice) took credit for bringing to "operational readiness" was an atomic apparatus improvised toward the end of May 1967, at a time when Israel was preparing burial sites for the thousands of victims the war was expected to create. In this Israel crossed a threshold the likes of which it had never crossed before.

This was the first time the nuclear project managed by Professor Dostrovsky had taken a series of emergency measures. Now, for the first, time, Israel had a real nuclear option. This move expressed the depth of Israel's existential anxiety at that time: If everything failed, and Israel's existence were on the brink, the nation would be able to evince a doomsday weapon.

To the best of my understanding, these emergency measures were not taken in answer to a specific request from the highest military or government levels, and certainly not as a response to a concrete operational need. They were taken simply because those who were doing the work were unable not to do so. The nuclear project had reached a historic point at which it was simply possible to do this, and those working on the project could not imagine that such steps should not be taken at that critical moment, even without an order from above.

To this day, if the published reports are correct, this dramatic event has not been included in the official history of the Six-Day War. To this day the State of Israel has not publicly expressed its thanks to Dostrovsky, Mardor, Joseph Tulipman (the director of the nuclear scientific complex during that period) and their staff. Within three hours, the Israel Air Force destroyed most of the air forces of the Arab countries - the rest is known. This dramatic move on the eve of the war evaporated from national memory as though it never happened. In other words, it was and remains taboo.

Prime minister Eshkol continued to maintain ambiguity with respect to the nuclear issue and apparently he found it hard to decide what Israel should do. New, far more urgent problems arose in the wake of the war and in any case, post-war Egypt was not the Egypt pre-1967. No one feared an Egyptian preventive strike against Dimona anymore, and after the decisions of the Khartoum summit, no one was looking for cracks for peace either. Meir Amit's fine diplomatic idea that the atom might perhaps be able to find an opening for peace breathed its last.

The signing of the NPT a year later did not ease Eshkol's hesitations either. He did not say yes to the NPT (as was the belief at the start of 1968), but he also did not say no to it; he simply kept postponing the decision. When he died, in February 1969, the issue had still not been resolved.

It was Eshkol's successor, Golda Meir, who after about a year of thought and discussions shaped the ambiguous path Israel walked with respect to the atom during the following decades. After years of hesitations and pondering, of wondering how and in what way others would react, Israel found a way, or a non-way, of preserving the nuclear legacy of 1967.

The writer is a senior research scholar at the University of Maryland and the author of "Israel and the Bomb."