A German publication asserted it has proof that submarines made by Germany for Israel have nuclear warfare capability.

The Jewish state’s procurement of a suite of German-made Dolphin submarines has been no secret, but critics of the deal brought up questions of nuclear armament. There were suspicions that the subs were designed so that nuclear weapons could be placed at the head of the vessels, a claim weekly magazine Der Spiegel said it can confirm.

Much of the publication’s evidence comes from testimony by two ex-officials. The magazine quoted former German State Secretary Lothar Rühl and former chief of the planning staff Hans Rühle as saying that, during their tenure, they assumed the submarines would be fitted with nuclear weapons.

Der Spiegel also quoted Israel Defense Minister Ehud Barak as saying that Germans should be “proud” that they have helped secure Israel’s existence “for many years.”

The publication claimed it had conducted “extensive research” on the subject, allowing it to state that the Jewish state was indeed in the process of equipping the vessels with nuclear warheads.

The Israeli government does not publically talk about its rumored nuclear program.

Earlier this year, German Nobel laureate Günter Grass drew criticism after publishing a poem accusing Israel of aiming to wipe out Iran. Grass also condemned the German government’s presumed culpability in such a goal, pointing to the submarine deal.

Four of the six subs commissioned by Israel have already been finished, with the final two to be delivered by the end of 2017. There are reports that the Jewish state might order more in the future.