Israel is bracing for possible retaliation from Iran after the assassination of Tehran’s close ally, Hamas leader Ismail Haniya, in the Iranian capital last week, heightening its fears that the war could spill over into the wider Middle East region.

Here’s a look at both countries’ air forces and air defense systems:

Iran’s war machine

The Iranian Air Force has 37,000 personnelbut international sanctions imposed on the country for decades have largely cut it off from modern high-tech military equipment, according to the International Institute for Strategic Studies in London (IISS).

The Air Force has only a few dozen operational aircraft, including Russian jets and older American models acquired before the 1979 Iranian revolution.

Tehran has a squadron of nine fighter jets F-4 and F-5a squadron of Russian-made Sukhoi-24 jets and some MiG-29, F7 and F14 jets, the IISS said.

The Iranians also have drones. Analysts estimate that Tehran’s drone arsenal numbers only a few thousand. In addition, they say, Iran has more than 3,500 surface-to-surface missiles, some of which carry half-ton heads. However, the number that may reach Israel may be less.

Iran’s Air Force commander said in April that the Sukhoi-24s were in the “best state of readiness” to deal with any possible Israeli attack.

But Iran’s reliance on Sukhoi-24 jets, which began in the 1960s, shows the relative weakness of its air force.

For defense, Iran relies on a mix of Russian and domestically produced surface-to-air missiles and air defense systems.

Tehran received S-300 anti-aircraft systems from Russia in 2016, which are long-range surface-to-air missile systems capable of engaging multiple targets simultaneously, including aircraft and ballistic missiles.

Iran also has the domestically produced missile platform ground-to-air Bavar-373, as well as the Sayyad and Raad defense systems.

Israel’s war machine

Israel has an advanced US-supplied air force with hundreds of multi-role aircraft F-15, F-16 and F-35. These played a role in the downing of Iranian drones in April, when the Islamic Republic launched drones and missiles into Israel in its first direct attack on Israeli soil.

The Air Force lacks long-range bombers, although a smaller fleet of redesigned Boeing 707s serve as refueling aircraft that could allow its fighters to reach precision targets in Iran.

Israel’s air force demonstrated its ability to strike long-range targets in July when its warplanes struck targets near the Yemeni port of Hodeidah in retaliation for a Houthi drone attack on Tel Aviv.

A pioneer in drone technology, Israel has Herons capable of flying for more than 30 hours, enough for long-range operations. The Delilah cruise missiles have an estimated range of 250 kilometers that they can reach – a long way from the Gulf, although the air force could minimize the distance by launching it closer to Iran’s border.

Israel is widely believed to have developed long-range surface-to-surface missiles, but has neither confirmed nor denied this.

A multi-layered air defense system developed with US help after the 1991 Gulf War gives Israel several additional options for shooting down Iranian drones and long-range missiles.

The Arrow-3 system is designed to intercept ballistic missiles outside the Earth’s atmosphere. An older model, the Arrow-2, operates at a lower altitude. The medium-range David’s Sling counters ballistic and cruise missiles, while the short-range Iron Dome counters the kind of rockets and mortars used by Iran-backed militias in Gaza and Lebanon – but can also, in theory, intercept missiles that escaped from Arrow or David’s Sling.