The arrival of a U.S. high-altitude defence battery — along with dozens of American troops — will help boost Israel's air defence systems, which, according to one Israeli defence expert, are straining under repeated attacks from Iran and its proxy in Lebanon, Hezbollah.

"Israel's air defence requires any help it can get especially if the war escalates and it turns into a war of attrition between Israel and Iran," said Ehud Eilam, who used to serve in Israel's military and is a long-time researcher of its security issues and defence policy.  

Israel's current, multi-layered defence system is designed to intercept incoming missiles and other projectiles at various altitudes and has, for the most part, protected cities and military installations that have come under fire during the past year from Iran, Hezbollah and Houthi militias in Yemen.

But as Israel gets set to launch retaliatory attacks against Iran — for its recent barrage of more than 180 ballistic missiles — there are concerns it will have to be ready for additional, significant attacks from that country, which has the largest missile stockpile in the Middle East

Israel, with the help of the U.S., intercepted most of the missiles in Iran's Oct. 1 attack. But, Eilam told CBC News, that they weren't all shot down likely means Israel is rationing its supply of interceptors. 

"Israel will have to calculate very carefully how many missiles it can use," Eilam said from Boston, where he is based.

"It definitely has a shortage of missiles."

Israel's air defence network is comprised of three different systems: the Iron Dome which shoots down short-range projectiles, including rockets launched from Gaza; David's Sling, which shoots down medium-range rockets, like those fired from Lebanon; and the Arrow system which has intercepted long-range ballistic missiles from Iran.  

The U.S.-made Terminal High Altitude Area Defense (THAAD) system will soon also be operational. 

That system can even intercept missiles flying above the earth's atmosphere. The battery, which can be repositioned as it is mounted on military vehicles, costs about $1 billion US and will be operated by 100 U.S. troops.

While the deployment is seen as a significant step by Washington, Eilam says he believes Israel and the U.S. can't keep producing missiles as quickly as may be required.

Israel is defending against attacks on multiple fronts, which is extremely costly. 

The country is ramping up its production of ammunition and other weaponry to arm its soldiers who have been fighting in Gaza since last year, and in Lebanon since the beginning of October. 

In an article by the U.K.-based Financial Times, the chief executive of Israel Aerospace Industries, which produces the missiles used for the Arrow system, said its production facilities are working 24 hours a day, seven days a week to try to meet demand.

Eilam says each Arrow missile costs about $3 million US. 

While ballistic missiles pose the greatest threat to communities and infrastructure, drones have proved challenging for Israel to defend against, as they are smaller, much slower and fly closer to the ground. They are also relatively cheap to produce, so they can be deployed en masse. 

Four Israeli soldiers were killed and dozens of others were wounded on Sunday after a drone crashed into the roof of a dining hall at a military base near the town of Binyamina-Giv'at Ada in central Israel.

"There was no alarm, I didn't hear a boom," said area resident Noam Weintraub, 20. 

"We have an amazing air defence system… but sometimes mistakes can happen and of course, as we get better, also the enemy gets better with their drones."

The Israeli military says it is investigating how the drone evaded the air defence systems.

Eilam says missile interceptors are sometimes not effective against drones.

And while a single drone won't cause anywhere near the damage of a ballistic missile, they can still be lethal, and Iran has a large supply of them, he says. 

Its drones have also been used by Russia — deployed throughout the war in Ukraine against cities and infrastructure. 

Drones "are like a terror weapon because they can come out of nowhere and just hit in the middle of some town," Eilam said. 

On Monday, several Israeli companies participated in a trial where they tested prototypes for intercepting drones. The field test took place in southern Israel, and included large defence contractors and startups. Israel's government said it will select several of the technologies to go through accelerated testing and production.