With the possibility of a major conflict brewing with the United States since the killing of Quds Force Commander Qasem Soleimani, the capabilities of the Iranian military are being sharply scrutinized.
So just how strong are the Islamic republic's armed forces?
The answer to that question hinges largely on what strategic goals Iran pursues.
Tehran’s main goal is to project its influence and protect its interests throughout the Middle East or to at least prevent adversaries, like Saudi Arabia, from gaining the upper hand.
To accomplish that, Tehran has done everything possible to deter and harass the enormous contingents of U.S. forces deployed in 10 countries throughout the region with the ultimate objective being to push them out.
In pursuing that goal, Iran will likely avoid a full-blown war because its military is no match for the American armed forces and Washington's allies stationed in the Middle East, experts say.
No Nukes, Lots Of Proxies
The Iranians have a well-publicized and highly controversial nuclear program, but do not currently have the capability to make a nuclear weapon.
"They have a ballistic-missile program but no long-range missiles that can reach the United States," The Atlantic noted.
It added that Tehran lacks any major friends in the region: "Iran has decent relations with Russia and China but no stalwart, great-power allies."
As arguably one of the world’s most-isolated countries, Iran has mainly embarked on a strategy of proxy wars or conducting asymmetrical strikes aimed at exploiting the vulnerabilities of American and U.S.-led forces.
The Iranian military -- which is the eighth largest in the world based on active personnel -- is suited to pursue a strategy of asymmetrical warfare.
Modest Military Budget
Iran's defense budget in 2018 was more than $13 billion, ranking it 18th in the world in terms of military expenditures, according to the Stockholm International Peace Research Institute (SIPRI).
But Tehran lagged far behind regional foes such as Saudi Arabia, which spent some $70 billion, and Israel, at $18.5 billion (the United States is without rival at more than $700 billion).
In addition, Iranian military expenditures declined by 9.5 percent in 2018 compared to the previous year due to massive economic problems caused by U.S. sanctions, a strategy that Washington refers to as "maximum pressure."
But Iran’s military establishment, especially the Islamic Revolutionary Guards Corps (IRGC), does not depend merely on the state budget for its funding, according to the Washington-based Foundation for Defense of Democracies (FDD).
"The military establishment controls [one-fifth] of the market value of companies listed on the Tehran Stock Exchange and owns thousands of other companies, all of which generate revenue for the armed forces," the FDD reported. "Additionally, the IRGC controls a significant portion of Iran’s underground economy."
Biggest In The Middle East
In terms of overall military strength, the Iranian armed forces rank 14th in the world out of 137 countries that are ranked in 2019 by Global Firepower and Business Insider.
With some 523,000 active-duty forces and another 350,000 reserves, Iran has the largest standing military in the Middle East.
The active forces are comprised of 350,000 in the regular army and at least 150,000 in the IRGC, which has the most powerful forces in the Iranian military.
In a sign of its importance, IRGC Commander in Chief Hossein Salami reports directly to Iranian Supreme Leader Ayatollah Ali Khamenei.
An Army Within An Army
The IRGC itself is made up of five subgroups.
One of those groups, the Quds Force, was led for decades by Soleimani until his assassination in a U.S. drone strike on January 3 -- the event that put Iran and the United States in their current quandary.
The Quds Force is mostly tasked with overseas operations, predominantly in the Middle East.
Estimates of its exact number of forces vary.
But Jack Watling, a research fellow at the Royal United Services Institute, told NBC News that it is a “divisional strength military formation” of around 17,000 to 21,000 members.
Perhaps more importantly, the extraterritorial use of the Quds Force provides for the enlistment of various Shi'ite militias that number, according to The Guardian, up to 200,000 fighters. The militias operate in at least five countries in the region.
The English daily adds that these pro-Iranian proxy armies that engage "in a 'grey zone' of conflict that maintains hostilities below the threshold of state-on-state warfare."
Another group within the IRCG structure is the Basij militia, a paramilitary force with 90,000 members mobilized to enforce order, which includes quelling dissent within the country, such as the nationwide anti-government protests in November that ended with hundreds of demonstrators killed and thousands injured.
Like many related institutions in Iran, the Basij was first formed as a volunteer force during the Iran-Iraq War. But it “has since become an entrenched, and feared, part of the state,” The Washington Post reported.
Also operating under the IRCG umbrella are the 20,000 service personnel in the naval forces, which rely first and foremost on waves of armed patrol boats in the Strait of Hormuz.
With more than 20 percent of the world's oil trade moving through the strait, it is the world's most-important oil-trade route and the scene of several confrontations between Iranian vessels and foreign-flagged tankers in 2019.
Although smaller in number, the IRCG is more powerful than the regular army because of the bifurcated nature of the Iranian state. For that reason, relations between the government and the IRCG have always been strained.
Iran has some 1,634 tanks, ranking 18th out of 137 countries surveyed. That number is buttressed by about 2,345 armored combat vehicles and 1,900 rocket launchers.
The large tank force is, however, mostly made up of older models and completely outdated tanks. Only the new model Karrar, which was supposed to be delivered to the Iranian military in 2018, can compare with some of the better tanks in the world. Although the Karrar looks much like the well-known Russian T-90, Iran has rejected suggestions there was any collaboration with Russia in its production.
In The Navy
The Iranian Navy is, comparatively, a modest force that has neither an aircraft carrier nor a destroyer.
Tehran's navy does possess six frigates, three corvettes, 34 submarines, and 88 patrol vessels. The submarine's arsenal contains the Russian-made "kilo" class, which are called "black holes" because they are inaudible.
The 'Fast Flyers'
With some 509 aircrafts, the Iranian Air Force lags far behind -- both in terms of quantity and quality -- regional adversaries Saudi Arabia and Israel, which can boast of having 848 and 595 state-of-the-art airplanes, respectively, in their fleets, The National Interest reported.
That doesn't include a healthy stable of U.S. planes throughout the region.
Much of Iran's air force dates from the shah era or is left over from dictator Saddam Hussein’s Iraqi Air Force, which moved many of its planes to Iran during the 1991 Persian Gulf War to avoid their destruction by U.S.-led forces.
American-made F-4, F-5, and F-14 fighters built in the 1970s remain the pillar of the Iranian Air Force, which is nicknamed "Tizparvazan" (the Fast Flyers).
Following the 2015 nuclear deal -- which lifted tough international sanctions against Iran and boosted its economy -- the country had a brief opportunity to upgrade its air force.
France's Mirage 2000 was an option, but Tehran ultimately decided against it because it was more familiar with its American- and Russian-made planes.
Iran also had a chance to buy as many as 30 sophisticated Su-30 fighters from Russia, but opted not to, The National Interest reported.
“This is probably because the Iranian Islamic Revolutionary Guards Corps paramilitary has never been comfortable with the regular Iranian military becoming too powerful,” the U.S. magazine concluded.
Crippled by the U.S.-imposed sanctions that have reduced its oil exports to a trickle, Iran's military equipment imports have dropped significantly in recent years.
Iran's arms imports decreased drastically in 2018 and the country's total imports for its military from 2009 to 2018 were just 3.5 percent of Saudi Arabia's total imports during the same period.
Tehran has had to therefore increasingly depend on the development of domestic technologies for its military needs, including cheaper hardware imports that come mainly from Russia and China.
Iran also relies on the development of missiles in order to overcome the disadvantage of having less military equipment that is often of a lower quality than its regional foes and, certainly, the United States and other Western countries.
Iran is, however, recognized as having the most developed short- and medium-range missile system in the region.
Among other missiles, it has 300-kilometer range Shahab 1 missiles, moving Washington to install a Patriot antiaircraft system in some neighboring countries to counter possible missile threats from Iran.
Tehran has also worked on the development of intercontinental missiles, although those programs were suspended after Iran agreed to the historic nuclear agreement with six world powers in 2015 that put curbs on its nuclear program.
Following the withdrawal of the United States from the treaty in 2018, Iran began to gradually suspend its adherence to the provisions of the treaty and ultimately announced after Soleimani's killing that it was abandoning all limits in the agreement.
That development leaves open the possibility of Tehran restoring efforts to develop intercontinental missiles.
According to the International Institute for Strategic Studies (IISS), a Shahab 3 missile with a range of up to 2,000 kilometers could hit Israel and is widely considered to be Tehran’s deterrent of last resort.
The International Institute for Strategic Studies also reports that Iran has 32 batteries of Russia's S-300 air-defense system.
Not To Forget: Cyberwarfare And Drones
Finally, Iran also has a full complement of drones that it has used in operations in both Iraq and against Israel. It is also believed that an Iranian drone was used in September to attack Saudi oil facilities.
The IRGC also boasts a cyberattack unit that is known to have been responsible for several attacks abroad.
After the assassination of Soleimani, many figured Iran could respond with a massive cyberattack against a U.S. entity, a fear that continues, according to The New York Times.
Most analysts have predicted that Iran would not venture into an open conflict with the United States over Soleimani's killing, but would instead use its assets to conduct asymmetrical operations to try and harm U.S. forces or American interests in the Middle East.
Despite having already responded with a missile attack against the two U.S. military bases in Iraq, the threat of lower-level attacks using other strategies remains.
In such a potential confrontation, Tehran would count on "three legs," as Deutsche Welle pointed out.
One leg is "defense before the border" -- namely the operation of Quds Force units outside Iran to attack U.S. forces.
The other legs of such a strategy are the use of long-range missiles to strike further away U.S. targets or an attempt to shut down the Strait of Hormuz and send global energy markets into a death spiral.
In the event of a conflict involving action in the Strait of Hormuz, Iran can count on the world's fourth-largest oil reserves of more than 150 billion barrels to sustain it during such a blockage.
Tehran's concern of a land invasion of its territory is probably quite low, as according to some Western estimates quoted by The Guardian, such an incursion would require “an improbable 1.6 million troops” in order to prevent an Iraq-style counterinsurgency from emerging against U.S. forces.
With U.S. President Donald Trump seemingly de-escalating after Iran's January 8 missile attack caused no American casualties, few people envision Washington entertaining a scenario involving ground troops.
U.S. Troops In The Region
There are estimated to be more than 50,000 U.S. troops deployed in the Middle East, according to numerous sources. Here is a rough breakdown:
Another possible option for Iran is the status quo.
Historian David Crist has dubbed the four decades of the shadow battle that the United States and Iran have been locked in since the 1979 Islamic Revolution to be a ''twilight war."
As The Atlantic noted, Iran has tended to follow a certain blueprint during this time: “compensate for its inferior military capabilities relative to the United States by waging wide-ranging proxy warfare that stops short of direct conflict, allows it to maintain plausible deniability, and is carefully calibrated to advance Iranian interests at a low cost and with minimal risk."
Soleimani's assassination by U.S. forces and the Iranian missile response hitting American bases in Iraq is the first open confrontation between the two countries since Iranian protesters invaded the U.S. Embassy in Tehran in 1979.
Although the current situation has de-escalated for the moment, it is still fraught with the risk of becoming more serious and disrupting the "twilight war" of strained but controlled relations that have existed between the two countries for so long.