Those following the turmoil in the Middle East might be surprised to hear of increasingly friendly relations between Israel and Saudi Arabia, longtime rivals that now face the shared threats posed by Iran’s nuclear program and the Islamic State of Iraq and al-Sham.

Last November, Saudi Arabia’s petroleum minister, Ali al-Naimi, expressed a willingness to sell oil to Israel, which it still does not formally recognize. “His Majesty King Abdullah has always been a model for good relations between Saudi Arabia and other states,” Naimi told reporters in Vienna, “and the Jewish state is no exception.” Just months earlier, former Saudi intelligence chief Prince Turki al-Faisal published an op-ed in the Israeli newspaper Haaretz. Although al-Faisal did little more than reiterate the Arab League’s traditional position on the peace process—namely that Israel withdraw to its pre-1967 borders—publishing in an Israeli newspaper represented a significant overture. These gestures followed years of speculation that Israel and Saudi Arabia might coordinate an attack on Iranian nuclear facilities.

However notable these developments are, unofficial cooperation between the two countries is hardly unprecedented. As early as the 1960s, Israel and Saudi Arabia found common ground when it came to countries or movements that explicitly threatened both of their existences. The two countries didn’t merely align their strategies, however; they collaborated on a tactical level, too.

During the 1960s, that threat emanated from Egyptian President Gamal Abdel Nasser, the leader of the Arab Nationalist movement and the most popular figure in the Middle East. His political speeches and radio broadcasts reached millions across the Arab world, and Israel, Saudi Arabia, and the United Kingdom were its frequent targets.

When a cadre of Yemeni officers with Arab-nationalist sympathies toppled Yemen’s theocratic monarchy in 1962, Nasser dispatched some 70,000 Egyptian troops to support the new republic’s war against old-regime loyalists. Nasser also declared his intention to carry the revolution even further, to Saudi Arabia, on Yemen’s northern border, and to the British colony of Aden, to the south.

Saudi Arabia, meanwhile, offered the royalist tribes money and refuge while a team of British mercenaries attempted to funnel military aid to anti-Egyptian forces on the ground. But northern Yemen’s mountainous terrain proved a major stumbling block, making it extremely difficult to deliver weapons and supplies to beleaguered tribal militias on the ground.

Since neither London nor Riyadh wanted to openly support the royalist forces, they needed a partner that would be willing to organize airlifts clandestinely over hostile territory. They turned to Israel, the only country with more to lose than Saudi Arabia from an Egyptian triumph in Yemen. Israeli leaders, for their part, believed that supporting a proxy conflict with Egypt would forestall an Egyptian-Israeli confrontation in the Sinai, keeping Nasser too preoccupied to attack Israel.

The celebrated Israeli transport pilot Aryeh Oz, then serving as the leader of Israel’s International Squadron 120, led the mission. Using a retrofitted Boeing Stratocruiser, he oversaw 14 flight missions to Yemen’s northern highlands between 1964 and 1966, carrying vital weapons and supplies that, in numerous cases, helped turn the tide of battle in favor of the royalists. Israeli pilots charted a flight path directly over Saudi territory, avoiding Egyptian fighter jets patrolling the Red Sea.

Planning and decision-making were limited to a select number of British mercenaries, Israeli leaders, Saudi royals, and the ousted Yemeni imam and his foreign minister. To ensure the safety and secrecy of the missions, they left the general Saudi and Yemeni populations in the dark about Israel’s involvement. One of the airdrops, for example, took place after the deposed leader had announced to his tribal leaders that supplies would be dropped from the sky. “Look, even God is helping the imam,” a British intelligence agent heard one of the commanders declare in the drop zone.

The civil war ended in 1968; following a series of agreements, the royalist and republican factions united to form the Yemen Arab Republic in the northern half of the country. If the Israelis and Saudis managed to put aside their differences back then, they certainly could do the same today. Both countries consider the prospect of a nuclear Iran just as threatening, if not more so, than they viewed the possibility of an Egyptian foothold in Yemen during the 1960s. And the danger is urgent enough that it could prompt tactical cooperation under certain circumstances, especially if Tehran appeared to be close to completing a bomb.

Moreover, five decades after the Israeli-Saudi airlifts in Yemen, unofficial ties between the two countries remain. For years now, Riyadh has turned a blind eye to imports of Israeli products, while Saudi businessmen have reportedly considered purchasing real estate in Tel Aviv through third parties. Speculation about secret diplomatic and security discussions continues.

Recent indications of a gradual warming of relations—and an uptick in backdoor dealings—are nothing new. Nobody should be surprised if they proceed even further, opening the door to a new era of regional cooperation.