The Israeli navy is getting two German-built frigates under a $1.37 billion contract that will build up its maritime firepower, officials said.

Their primary mission is expected to be protecting the Jewish state's rich natural gas fields in the eastern Mediterranean.

The warships, which the Israelis are expected to pack with their own weapons and electronic systems, such as the Barak 8 medium-range air defense system produced by Israel Aerospace Industries, will be the most advanced surface vessels in the Israeli navy.

The frigates will reinforce three advanced Super Dvora Mark III missile corvettes, known as Sa'ar 5s, currently on order from state-run IAI's shipyards in Haifa. These ships will join four already in service and will be primarily deployed to shield the offshore fields that currently contain an estimated 30 trillion cubic feet of natural gas, with more expected that will earn an estimated $150 billion in export revenue over the next two decades.

That makes the gas fields, and the attendant production infrastructure, a high-value strategic asset that will transform the country's economy after decades of dependence on imported energy.

The German vessels are believed to be MEKO class F221 frigates developed by Blohm + Voss at their Hamburg yards equipped with 76mm guns, surface-to-air missiles, torpedoes and Harpoon anti-ship missiles.

Defense sources say the Israelis were split between buying four low-end corvettes or two high-end frigates, but opted for the more advanced vessels because they can undertake other missions, such as countering the growing submarine threat in the Mediterranean and the Red Sea.

Iran has said it will deploy its Russian-built Kilo-class submarines in these waters, while Egypt is negotiating with Germany to acquire at least two Type-209 diesel-electric attack submarines produced by Howaldtswerke-Deutsche Werft AG of Kiel.

HDW also builds the advanced Dolphin-class submarines deployed by the Israeli navy, with four operational and two more under construction. The Dolphin is based on the Type-209 but with classified Israeli missiles and electronic systems.

The 7,000-strong Israeli navy, long the Cinderella service of the armed forces, has been expanding at a time when Israel's defense budget is being heavily cut.

That situation could change once gas exports get underway, possibly via underwater pipelines to Turkey or Europe, or via liquefied gas terminals from which exports are shipped by tanker.

The Israeli press has reported on more than one occasion that the cost of bolstering the navy's capabilities could be partly underwritten by state-owned companies involved in constructing and operating the gas field infrastructure.

In April, Capt. Ilan Lavi, director of the Israeli navy's planning division, said the new offshore gas industry offers Israel's adversaries a tempting target whose destruction would have a strategic impact on Israel's economy.

"We have to build an entirely new defensive envelope," he said.

The navy has been gradually building up patrols around the gas fields, primarily the largest fields, Leviathan and Tamar off the coast of northern Israel.

Tamar, with some 8.4 trillion cubic feet of gas, began production in March. Leviathan, which covers around 125 square miles and contains around 17 trillion cubic feet of gas, is expected to follow in 2016.

Security concerns grew this year when Russia supplied Syria with 72 supersonic Yakhont anti-ship missiles, some of which the Israelis fear could be handed over the regime's Lebanese ally Hezbollah.

The Yakhonts have the range to reach the Israeli gas fields, particularly if fired from south Lebanon.

"Another danger is a proximity attack, by frogmen, by boats, by terrorists in some fashion," Gen. Giora Eiland, a former Israeli national security adviser, told the Globes business daily recently.

Hezbollah, backed by Iran and Syria, is viewed as a particular threat.

Its guerrillas drove Israeli forces out of south Lebanon in May 2000 to end 22 years of occupation and fought Israel's vaunted military to a standstill in a 34-day war in 2006. Hezbollah is currently believed to have an arsenal of more than 60,000 missiles and rockets.

In February 2012, the Israeli navy seized an Iranian arms shipment that authorities said was bound for the Palestinian Hamas group in the Gaza Strip bordering southern Israel. It contained 50 tons of arms, including six Nasr-1 radar-guided anti-ship missiles.