Some months ago it became known that the German Intelligence Service (Bundesnachrichtendienst - BND) was spying on Turkey. Turkey's political leadership was none too happy. Yet the BND has good reasons to keep a watchful eye on Ankara. It is not only the crises in Iraq and Syria, drug-smuggling, people-trafficking and the activities of the PKK that make Turkey a legitimate target for German intelligence. For quite some time, evidence is mounting that Ankara is trying to acquire nuclear weapons.

Over the past two decades, discussions within the nuclear community about emerging nuclear powers always centred on the "usual suspects": Iran, Saudi Arabia, Brazil, Egypt, Japan, South Korea and Turkey. Not surprisingly, opinions as to the likelihood of a military nuclear program differed. In the case of Iran, for example, the evidence appeared solid. By contrast, the case of Turkey was built on vague indications.

This list of likely nuclear aspirants has not changed since, yet the likelihood of a Turkish nuclear weapons program has increased dramatically. Simply put: the Western intelligence community now largely agrees that Turkey is working both on nuclear weapon systems and on their means of delivery. Iran is the model to emulate. Consequently, Turkey has started a large-scale civilian nuclear program, justified by the country's urgent energy needs. In 2011, Turkey concluded a $20bn contract with the Russian company ROSATOM on a large reactor complex. Two years later, a similar agreement was concluded with a Japanese-French consortium, this time over $22bn. President Erdogan also announced yet another power plant, to be built entirely by indigenous personnel.

So far, so good, one might say. After all, nuclear energy seems like a sensible option to at least partially meet Turkey's demand for affordable energy. However, a thorough analysis of the contracts reveals that these projects are not just about improving Turkey's energy supply. Turkey has also consciously opened the door to a military nuclear option.

Proposals for constructing a light-water reactor usually consist not just of a commitment to build the plant according to agreed specifications and timelines, but also commitments to run the project for sixty years, to provide the required low enriched uranium and to take back the spent fuel rods. Such offers were put forward by both Rosatom and the Japanese-French consortium. However, in both cases, Turkey insisted that the deal would neither include the provision of uranium nor the return of the spent fuel rods. Ankara wanted to deal with this matter separately at a later stage. Turkey never provided an explanation for this decision. However, the intention behind this unusual maneuvering is not difficult to fathom. Turkey wants to maintain the option to run the reactors with its own low enriched uranium and to reprocess the spent fuel rods itself. This, in turn, means that Turkey intends to enrich uranium, at least to a low level.

And there is more. The option to provide low enriched uranium to currently eight agreed reactors—Turkey is planning twenty-three projects in total—indicates the scope of Turkey’s envisioned enrichment effort. The path that Turkey wants to take is clear: to follow in Iran’s footsteps. According to President Rouhani, Iran wants to build sixteen reactors by 2030, which are supposed to be powered by indigenously enriched uranium, although much of this low enriched uranium is earmarked for high enrichment and thus for the production of weapons-grade fuel. Of course, Turkey vehemently denies any intention to enrich uranium. However, Turkey has declared on many occasions that it will always insist on its “rights” deriving from the Nuclear Non-Proliferation Treaty (NPT), and that it regards enrichment for peaceful use as perfectly legal. That the Turkish government is at pains to justify its rejection of an external supply of low enriched uranium while not admitting a national interest in enrichment was illustrated by a statement made by the Turkish Minister for Energy, Taner Yildiz, in January 2014. Yildiz argued that the refusal to contractually settle the uranium supply with the aforementioned companies was due to Turkey’s desire to understand the full nuclear fuel cycle. Not only does Yildiz’ explanation appear weak; Turkey’s declaratory nuclear policy also seems to follow the path taken by Iran: one only admits what in light of the facts can no longer be denied.

Turkey’s motives for rejecting the continuous uranium supply by its Russian and Japanese-French business partners may appear dubious; its rejection to return the spent fuel rods to the supplying countries is outright disastrous, as it allows for only one conclusion: Turkey is bent on producing plutonium for making weapons. While reprocessing would indeed allow the reuse of the spent uranium, such an option is merely theoretical, since fuel rods made from reprocessed material are far more expensive than those made from “new” uranium. It is for this reason that reprocessing of spent uranium is hardly being conducted anymore.

With its rejection to return the spent fuel rods, Turkey is embarking on the pathway to the bomb. The common counterargument, according to which the separation of the “dirty” plutonium would require a sophisticated reprocessing plant that currently does not exist in Turkey, remains unconvincing. Studies have shown that such a plant can be built within half a year and would be the size of a regular office building. Moreover, the widespread belief that in order to build a nuclear weapon, one requires weapons-grade plutonium with an impurity level of at most 7 percent, is long obsolete. Already in 1945, General Groves, the leader of the “Manhattan Project,” noted that due to the shortage of pure plutonium, the United States would soon be forced to use material with an impurity level of up to 20 percent. In 1962, the United States detonated a plutonium bomb in Nevada that had an impurity level of 23 percent. Finally, if the fuel rods of a light water reactor do not remain inside the reactor for several years, which is the economically viable option, but are removed after only six to twelve months, one ends up with weapons-grade plutonium. The Iranian reactor Bushehr offers a telling example. If the reactor were powered down after eight months and the fuel rods removed, Iran would own 150 kilogrammes of plutonium with an impurity level of only 10 percent—the equivalent of twenty-five Nagasaki-category bombs. In short, the weaponization of plutonium has many facets.

The assumption that Turkey is aiming for nuclear weapons is also supported by the country’s activities towards creating the entire nuclear fuel cycle. As has been revealed by a well-connected information service, German intelligence reported that as far back as May 2010, Prime Minister Erdogan had demanded to secretly start preparing for the construction of sites to enrich uranium. Accordingly, Turkey has started to produce Yellowcake, a chemically compressed uranium ore. Yellowcake is converted to gas, which is then enriched in centrifuges. To date, nothing is publicly known about a conversion plant in Turkey, yet according to the BND, Turkey is already in possession of enriched uranium originating from a former Soviet republic and smuggled via Kosovo and Bosnia and Herzegovina with the help of the Mafia. It would not come as a surprise if Turkey already had centrifuges to enrich uranium. After all, Turkey was involved in the activities of Pakistani nuclear smuggler Abdul Qadeer Khan, who between 1987 and 2002 sold thousands of centrifuges to Iran, North Korea and Libya. The electronics of these centrifuges came from Turkey. Khan had even contemplated moving his entire illegal production capacity of centrifuges to Turkey. In 1998, then Pakistani prime minister Nawaz Sharif offered Turkey a “nuclear partnership” on nuclear research. Moreover, there is still an organic partnership between both countries dating back to Turkey’s support for Pakistan’s nuclear program. Back then, many of the components that Pakistan could not acquire openly were shipped via Turkey to Pakistan. With this backdrop, it does not come as a surprise when intelligence services report that to this day there is a dynamic scientific exchange between both countries.

The question of whether Turkey already has centrifuges and where they may have come from can probably be answered without the recourse to any revelations by intelligence services. At the same time, this might help solve one of the last enigmas of the history of nuclear proliferation: the search for the “fourth customer” of A.Q. Khan. In mid-2003, a shipment of centrifuge parts and tools intended for Libya “disappeared” during a journey from Malaysia via Dubai to Tripoli. It had been ordered—and probably already paid for—by President Gaddafi as part of a major deal on 10,000 centrifuges intended to turn Libya into a nuclear power. The sender of the shipment was A.Q. Khan, who had ordered a company in Malaysia to buy the components from all over the world and ship them to Libya.

Although the International Atomic Energy Agency (IAEA) tried for years to solve that case, what happened to this shipment could never be determined. Still, the IAEA could not simply drop that case, since the disappearance of this shipment could only mean one thing: in addition to the well-known three customers of A.Q. Khan, there must have been yet another. Accordingly, many experts refer to a mysterious “fourth customer.”

The enigma about the “fourth customer,” who appears to work on a nuclear option with utmost secrecy, has never been solved, even though a resolution appears to become ever more urgent. If one compares Pakistan’s production volumes with the production that Khan sold to his three customers beyond Pakistan’s own national needs, one finds considerable discrepancies. In other words, the “fourth customer” has received much more from Khan than just the one shipment originally intended for Libya. Khan, however, remains silent. Considering that, according to intelligence sources, Turkey is in possession of a considerable number of centrifuges of unknown origin, and considering that Khan, shortly before he was put under house arrest, had travelled to Turkey, the conclusion that Turkey is the fourth customer does not appear far-fetched.

Yet this may only be one part of the story. Khan not only delivered centrifuges to his customers, he also supplied them with blueprints for the design of nuclear weapons. The CIA uncovered such plans in Libya in 2003, which had been kept in a department store plastic bag. And in the course of investigating Saddam Hussein’s nuclear activities, the IAEA found a one-page document in 1998 that turned out to be a comprehensive offer by Khan to turn Iraq into a nuclear-armed power within three years, for the price of 150 million dollars. This offer explicitly referred to providing Iraq with all necessary components and blueprints for making nuclear weapons.

If Turkey had indeed been the “fourth customer” of the Pakistani nuclear smuggler, one must assume that the country is now in possession of all documentation necessary to build a bomb. And even if Turkey had not been the fourth customer, one must assume that, given the long cooperation on the production of centrifuges, Khan did instruct his preferred partner not just in how to use centrifuges, but also in weaponization.

Given the ambiguities surrounding the level of nuclear expertise of Turkish scientists, it remains difficult to offer clear-cut facts about the current state of Turkey’s nuclear activities. What appears worrying, however, are statements from intelligence circles about an advanced nuclear program. According to some sources, Israeli prime minister Netanyahu informed then Greek prime minister Papandreou on March 15, 2010 that Turkey could become a nuclear power any time it wanted to.

Another indirect piece of evidence for the existence of a Turkish nuclear-weapons program is Ankara’s missile program. For a long time, Turkey appeared content with developing short-range missiles with a range of up to 150 km. However, over the past years, various public statements indicate a change of course. Much publicity was given to a December 2011 statement by President Erdogan, in particular his demand to the Turkish defence industry to develop long-range missiles. While Turkish media interpreted Erdogan’s statement as a plea for intercontinental ballistic missiles, it remained unclear whether the president was really thinking in these terms. However, two months later, Turkey appears to have started developing a medium-range missile with a range of 2500 km. In 2012, Turkey tested a missile with a range of 1500 km, and it also became known that the missile with a range of 2500 km would be operational by 2015.

Even if Turkey will not be able to keep these deadlines, its intention to develop medium-range missiles is clear. This raises the question as to the strategic rationale of such weapons. The answer is fairly simple: Medium-range missiles only make sense with a nuclear payload. Thus, Turkey’s development of medium- or long-range missiles can only be explained in the context of a nuclear-weapons program. In a nutshell, Turkey’s desire to build missiles with longer ranges is a strong piece of evidence for the existence of a nuclear program.

But what are the views of Turkey’s political leadership on this issue? There are, of course, no public statements arguing the case for a national nuclear option. However, some statements can be interpreted as conditioned statements of intent. In August 2011, Turkey’s ambassador to the United States, Namik Tan, said: “We cannot tolerate that Iran obtains nuclear weapons.” This position was made more concrete two years later by President Abdullah Gül. In an interview with the journal Foreign Affairs, Gül said that “Turkey will not allow that a neighbouring country has weapons that Turkey itself does not have.” Since it should be clear by now to Turkish politicians that Iran, irrespective of the deal with the P5+1, will continue to pursue a nuclear program, there is no point anymore in conditioning one’s own nuclear work. Domestic hurdles appear low: In a 2012 poll, 54 percent of the 1500 people interviewed were in favor or Turkish nuclear weapons if Iran went nuclear.

Given these developments, it becomes clear why Turkey is a legitimate target for German intelligence. A NATO ally who appears to increasingly envision its own role as that of a nuclear-armed regional heavyweight is a development of tremendous importance that Germany cannot afford to ignore. Given Erdogan’s vision of Turkey as a self-confident, assertive and potentially independent regional leader in the Middle East, and given the existence of an established (Israel) and an emerging nuclear power (Iran), Turkey has no real alternative but to acquire nuclear arms as well. If Turkey does not opt for nuclear weapons, it will remain second class—a position that Erdogan cannot and will not accept.

Hans Rühle is a former Head of the Planning Staff in the German Ministry of Defense. He publishes frequently on security and defense matters.

Editor’s Note: This is the modified version of an article that was first published in the German newspaper “Welt am Sonntag"