The United States and Israel formally signed the new $38 billion 10-year “memorandum of understanding” (MOU), in what the State Department called the “single largest pledge of bilateral military assistance in U.S. history,” at the U.S. State Department on Wednesday.

The pact was signed by U.S. Undersecretary of State for Political Affairs Thomas Shannon, Jr. and Israel’s Acting National Security Adviser Jacob Nagel. National Security Adviser Susan Rice, Ambassadors Dan Shapiro and Ron Dermer also attended the signing ceremony.

Under the agreement, Israel will get $3.8 billion dollars annually, $500 million of which will be allocated to developing missile defense systems. Israel also committed not to approach Congress for additional budgets for missile defense systems, and “volunteered” to give back any money Congress gives above the MOU’s limits, according to The Washington Post.

But senior administration officials told Haaretz that in the event of an emergency, such as a war, the United States would be prepared to consider increasing the budget for missile defense systems beyond what is promised in the agreement, as it has done in the past.

President Barack Obama boasted that the new MOU “constitutes the single largest pledge of military assistance in U.S. history,” in a statement released after the signing ceremony. “Both Prime Minister Netanyahu and I are confident that the new MOU will make a significant contribution to Israel’s security in what remains a dangerous neighborhood,” the president said.

Israeli Prime Minister Benjamin Netanyahu hailed the deal as “unprecedented.”

“I would like to thank President Obama and his administration on this historic agreement,” Netanyahu said in a statement. “I also thank our many many friends in the US Congress, and the American people, for the greatest support which cuts across political parties and embraces the length and breadth of the United States.”

“The agreement will help us continue to build our armed forces and to continue to improve our anti-missile defenses,” the prime minister continued. “Many of the people in the US understand that Israel’s security investment strengthens stability in the Middle East, and it serves not only our security interests but also the security interests of the United States.”

In a statement on Tuesday, AIPAC commended President Obama and his administration “for forging this landmark agreement. It demonstrates America’s strong and unwavering commitment to Israel.”

Democratic presidential nominee Hillary Clinton welcomed the new security assistance deal as sending a clear message to the region and the world that the U.S. “will always stand shoulder-to-shoulder with Israel.”

“America’s commitment to Israel’s security must always remain rock-solid and unwavering,” Clinton said in a statement. “That’s why Senator Kaine and I applaud the agreement on a new memorandum of understanding regarding American security assistance to Israel, and congratulate Prime Minister Netanyahu and President Obama on this important diplomatic achievement. It reaffirms the depth and strength of the U.S.-Israel relationship — which is based on common security interests, shared values, and deep historical ties — and sends a clear message to the region and the world that we will always stand shoulder-to-shoulder with Israel.”

According to the Democratic nominee, the MOU “will help solidify and chart a course for the U.S.-Israeli defense relationship in the 21st century as we face a range of common challenges, from Iran’s destabilizing activities to the threats from ISIS and radical jihadism, and efforts to delegitimize Israel on the world stage.“