To Iranian Supreme Leader Ayatollah Ali Khamenei, Arak is much more important than Assad.

Arak, the site of Iran’s heavy water reactor, as well as Iran’s other nuclear installations at Natanz and Fordo would become dangerously exposed to a potential future attack if Iran goes into war against the United States to protect Syrian President Bashar al-Assad. With Russia dismantling and scrapping the S-300 anti-aircraft missiles which Iran bought and made a down payment on in 2007, Iran needs to keep what remains of its anti-aircraft system at home. It cannot afford to send them to Syria to help Assad’s army. The same goes for Iran’s missiles and fighter aircraft, especially the latter, because sanctions have reduced their numbers and quality over the years. Sending them abroad to help Assad against the United States would risk their loss, knowing full well that it will be extremely difficult if not impossible to replace them.

These are important reasons why, in case of a military attack by the United States against Syria, there is little chance that Iran will become directly involved. This is despite Iran stating that it would consider such an attack as crossing its “red line.”

There are also historical reasons which back the theory that Iran is likely to stay away. Despite several reported attacks by the Israeli air force against Assad’s military and in one case nuclear installations, Iran never became involved in a war against Israel to defend Assad. Iran’s military leadership is well aware that such a war would have exposed its nuclear installations and its military hardware to attacks by the Israeli air force. If Iran did not want to confront Israel because of Assad, its very unlikely that it would want to confront the United States, which has a far bigger and more powerful military arsenal.