David's Sling, being developed by Rafael Advance Defense Systems, isn't expected to be operational until 2013 but another Rafael air-defense system, Iron Dome, has already been deployed.
It's designed to shoot down short-range missiles and rockets and has done so with considerable success in recent months.
David's Sling, sometimes known as Magic Wand, is intended to counter medium-range missiles, such as cruise missiles, and is considered more effective in defending offshore platforms.
The navy is operating Israel Aerospace Industries Heron drones for maritime surveillance that includes the gas fields.
"The area we'll need to protect at sea will significantly increase with the construction of the new gas rigs," a senior naval officer told The Jerusalem Post.
The main gas fields in the eastern Mediterranean are Leviathan, 80 miles west of Haifa, a major Israeli port and naval base, and Tamar, 50 miles off Israel's northern coast.
These fields, discovered in 2009-10, are of immense strategic value to Israel because they make the Jewish state energy-independent. So they present important targets for the country's enemies.
Leviathan contains an estimated 16 trillion cubic feet of gas and Tamar 9 tfc.
The resources will transform the economy of Israel, which has had to import virtually all of its energy requirements, when they start producing. Tamar is scheduled come on-stream in 2013 and Leviathan by 2017.
The Israeli navy hasn't decided what missile defense system it will deploy offshore. Apart from David's Sling, it has been considering the Barak-8 system, developed and built by state-owned IAI. That system is used on naval vessels to intercept anti-ship cruise missiles.
Israel's naval commanders are particularly concerned about Syria's acquisition of two Russian-built coastal-defense Bastion anti-ship systems with 72 supersonic Yakhont SS-N-26 cruise missiles that significantly bolster Syria's naval capabilities.
Russia's Interfax news agency said the missiles were ordered under a 2007 contract worth an estimated $300 million.
The Yakhont delivery caused considerable alarm in Israel, which has long outgunned Syrian naval forces.
The SS-N-26, with a range of 190 miles and a maximum speed of Mach 2.5, carries a warhead of 440 pounds of high explosive, enough to sink a large warship, such as an aircraft carrier.
Such a weapon could pulverize an offshore gas platform.
The Yakhont's nearest U.S. counterparts, Raytheon's BGM-109 Tomahawk and Boeing's AGM-84 Harpoon, are subsonic. The best French equivalent, MBDA's MM-40 Exocet, only has a range of 45 miles.
The Israelis say they fear some of the Yakhonts could end up in the hands of Hezbollah, Iran's main proxy in Lebanon and a key Syrian ally.
While Middle East security experts doubt that, given the need to protect the Russian naval base being built at Tartous, one of Syria's main ports, Syria has provided Hezbollah with thousands of missiles and rockets in recent years.
In the opening phase of the 2006 war between Hezbollah and Israel, the Iranian-backed Shiite movement seriously damaged an Israeli corvette off the Lebanese coast with a Chinese-designed C-801 missile provided by Iran via Syria.
On March 15, 2011, the Israeli navy intercepted the Liberian-flagged freighter Victoria carrying 50 tons of Iranian weapons reportedly destined for the Palestinian Islamic Jihad militant group operating in the Gaza Strip.
The arms included six Chinese-designed C-704 radar-guided anti ship missiles the Iranians call the Nasr. It carries a warhead containing 280 pounds of high explosive.
The protection of the gas fields and their infrastructure gives the navy responsibilities and it's seeking new ships and equipment at a time when Israel's armed forces are having to cope with hefty cuts in defense spending.
"Until now, the navy had focused on protecting Israel's sea lines of communication, which span the length of the Mediterranean and around the Maghreb region of North Africa," the Post observed.
"Some 99 percent of all goods arriving in the country come by sea, including security-related supplies and military hardware."
The navy is thus seeking to acquire four new warships larger than the Sa'ar-class corvettes it currently operates. For budgetary reasons, these will likely be built by Israel Shipyards in Haifa than bought from abroad.