KSA just put in a huge order for U.S.-made anti-tank missiles that has Saudi-watchers scratching their heads and wondering whether the deal is related to Riyadh’s support for the Syrian rebels.

No one is expecting a tank invasion of Saudi Arabia anytime soon, but the kingdom just put in a huge order for U.S.-made anti-tank missiles that has Saudi-watchers scratching their heads and wondering whether the deal is related to Riyadh's support for the Syrian rebels, Foreign Policy reported.

The proposed weapons deal, which the Pentagon notified Congress of in early December, would provide Riyadh with more than 15,000 Raytheon anti-tank missiles at a cost of over $1 billion. According to the International Institute for Strategic Studies' Military Balance report, Saudi Arabia's total stockpile this year amounted to slightly more than 4,000 anti-tank missiles. In the past decade, the Pentagon has notified Congress of only one other sale of anti-tank missiles to Saudi Arabia -- a 2009 deal that shipped roughly 5,000 missiles to the kingdom.

"It's a very large number of missiles, including the most advanced version of the TOWs [tube-launched, optically tracked, wire-guided missiles]," said Jeffrey White, a fellow at the Washington Institute for Near East Policy and a former intelligence analyst at the Defense Intelligence Agency. "The problem is: What's the threat?"

That's a tough question to answer. A military engagement with Iran, the most immediate potential threat faced by Riyadh, would be largely a naval and air engagement over the Persian Gulf. Saudi Arabia has fought a series of deadly skirmishes with insurgents in northern Yemen over the years, but those groups have no more than a handful of military vehicles. And Iraq, which posed a real threat during Saddam Hussein's day, is far too consumed by its internal demons and the fallout from the war in Syria to ponder such foreign adventurism.

But one Saudi ally could desperately use anti-tank weapons -- the Syrian rebels. In the past, Riyadh has been happy to oblige: It previously purchased anti-tank weapons from Croatia and funneled them to anti-Assad fighters, and it is now training and arming Syrian rebels in Jordan. Charles Lister, a London-based terrorism and insurgency analyst, said that rebels have also received as many as 100 Chinese HJ-8 anti-tank missiles from across the border with Jordan -- and indeed, many videos show Syrian rebels using this weapon against Bashar al-Assad's tanks.

While most of the rebels' anti-tank weapons were seized from Assad's armories, Lister also believes that several dozen 9M113 Konkurs missiles, an old Soviet weapon, were provided to Islamist rebels in northern Syria this summer. And when these missiles have found their way to the battlefield, they've helped the rebels break through the belts of armor Assad uses to protect strategic areas: "Neutralizing these external defenses has proven key to opening the gates for ground assaults," Lister said.

The Saudis can't send U.S. anti-tank missiles directly to the rebels -- Washington has strict laws against that. Recipients of U.S. arms are not allowed to transfer weapons to a third party without the explicit approval of the U.S. government, which in the case of Saudi Arabia has not been granted. Given Washington's heightened concern over radical Islamist forces seizing control over the conflict -- which resulted in the suspension of nonlethal aid to Syrian rebels on Dec. 12 -- that approval will almost certainly never be given. If Riyadh went ahead and transferred the weapons anyway, it "would be a serious breach of U.S. law," said Aram Nerguizian, a senior fellow at the Center for Strategic and International Studies, that would "all but certainly lead to a suspension of existing arms sales agreements." So far, only one American anti-tank missile has been identified in Syria -- an older model that Lister speculates may have been sold to Shah-era Iran, transferred to the Assad regime, and then captured by the rebels.

But while the latest American anti-tank weapons might not be showing up in Aleppo anytime soon, that doesn't mean the deal is totally disconnected from Saudi efforts to arm the Syrian rebels. What may be happening, analysts say, is that the Saudis are sending their stockpiles of anti-tank weapons bought from elsewhere to Syria and are purchasing U.S. missiles to replenish their own stockpiles. "I would speculate that with an order of this size, the Saudis were flushing their current stocks in the direction of the opposition and replacing them with new munitions," said Charles Freeman, a former U.S. ambassador to Saudi Arabia.

Regardless of how this purchase of anti-tank missiles relates to Syria, it's undoubtedly part of a larger Saudi arms buildup that has been going on for nearly a decade. From 2004 to 2011, according to a 2012 report by the Congressional Research Service, Riyadh signed $75.7 billion worth of arms transfer agreements -- by far the most of any developing nation. The United States was the major benefactor of this Saudi largesse, as the deals bumped up U.S. arms sales to a record $66 billion in 2011 alone.

How the Saudis plan to use many of these weapons is a mystery. And it's not just the anti-tank missiles whose purpose remains unclear. Riyadh recently bought advanced fighter jets from the United States for a whopping $30 billion -- but the Saudis' lack of pilots and ability to maintain them means that it's an open question how long they can keep them airborne, said William Hartung, the director of the Arms and Security Project at the Center for International Policy.

But purchasing the weapons, rather than any intent to use them, may be the point for the Saudis. At a time when they are at odds with Washington over the Obama administration's diplomacy with Iran and nonintervention in Syria, the kingdom's deep pockets can at least make sure their ties to the Pentagon remain as strong as ever.

"There was a [Washington] lobbyist who used to say, 'When you buy U.S. weapons, you're not just buying the weapon -- you're buying a relationship with the United States,'" said Hartung. "I think that's kind of the concept."