In fact, Moscow did reinforce its troops along the Iranian border, even relocating nuclear howitzers from Eastern Europe along with SA-11 Gadfy surface-to-air missile systems, which had just entered service.

“Experts doubt that the Soviets would deploy most of their SA-11s to their southern borders – weakening the defenses against China and NATO – unless they seriously expected a military confrontation in Iran,” Anderson wrote.

But the defensive nature of the hardware the Soviets deployed indicated that they were more likely “preparing for counterattack rather than an invasion of their own.”

The New York Times reported in 1986 that the Soviet redeployments in 1980 were a major catalyst in the Pentagon’s creation of the so-called Rapid Deployment Force, a loose grouping of fast-moving ships, planes and paratroopers. U.S. Central Command, which would eventually oversee the U.S. wars in Iraq and Afghanistan, grew out of the Rapid Deployment Force concept.

The earlier Soviet invasion of Afghanistan also pushed Carter to announce the “Carter Doctrine” in his State of the Union address in January 1980, the same month the Shah fled Iran.

“An attempt by any outside force to gain control of the Persian Gulf region will be regarded as an assault on the vital interests of the United States of America, and such an assault will be repelled by any means necessary, including military force,” Carter said.

However, the president’s actions in early 1980 actually conveyed weakness. He dispatched 12 F-15 Eagle fighters to Saudi Arabia in an attempt to reassure Riyadh following the Shah’s departure. The move embarrassingly backfired when the Pentagon revealed the jets weren’t actually armed. The subsequent failure of the Eagle Claw rescue attempt reinforced this image of weakness.

The Economist in March 1980 theorized that the Soviet Union might attack Iran in a bid to seize its oil fields while Washington and Tehran were locked in a standoff and Washington’s position in the region was significantly weaker than Moscow’s was. The Soviet presence in Afghanistan placed Soviet forces close to Iran’s major oil fields.

An op-ed in The Cincinnati Enquirer in April 1980 claimed that once American intelligence got wind of an imminent Soviet invasion, U.S. airborne troops would secure Iran’s oil in a preemptive intervention. “The Soviets then would know what might be the full implications of what they were about to do,” said one unnamed Washington source the article cited.

When the Soviet mouthpiece Pravda claimed the United States was preparing to invade Iran in January 1981, the Carter administration, at the time in final negotiations to release the hostages, staunchly denied it. As Reagan took the oath of office, Tehran released the hostages.

It’s not completely unlikely the Soviets really believed the United States would invade. Henry Trofimenk, the department chief of Moscow’s U.S.-Canada Institute, told a Swedish daily in July 1983 that fears of a U.S. invasion of Iran motivated the Soviet Union’s invasion of Afghanistan.

“We feared the United States would invade Iran, that was the true reason [we invaded Afghanistan],” Trofimenk claimed. “The U.S. had concentrated enormous forces in the Arabic Sea [sic] and the Indian Ocean,” he added, pointing out that the students took the Americans hostage in early November 1979 and the Soviets invaded Afghanistan the following month.

A secret 106-page Pentagon blueprint, first disclosed by the press in 1983, outlined how a world war could break out as a result of a Soviet invasion of Iran. While the document explicitly states that it “is not a prediction of future events nor a guide for the employment of forces,” it nevertheless showed how seriously the Pentagon was considering the fallout from Soviet action in Iran.

In the scenario, the Red Army invades Iran with 24 divisions. Saudi Arabia allows U.S. troops to deploy to the kingdom. Dogfights break out between the U.S. and Soviet air forces. Then the Soviets pour 90 divisions into Central Europe as NATO and the Warsaw Pact go to war. To make matters worse, North Korea then seizes the opportunity to attack South Korea.

Incidentally, the 1984 apocalyptic movie Threads depicts a nuclear war beginning between the United States and the Soviet Union after the Soviets invade Iran.

On Sep. 22, 1980, Iraq launched its ill-fated invasion of Iran’s oil-rich, Arab-majority Khuzestan province. The war lasted for most of the 1980s and killed millions. Nearly a year before the actual invasion, a brief border clash fueled rumors of an Iraqi attack.

Journalists Rowland Evans and Robert Novak, reporting from the Iran-Iraq border in December 1979, confirmed that there was no war yet, but there was “ready evidence of Iraq’s military confidence and power.”

In fact, the Iraqis at that time overestimated their military capabilities. The two journalists interviewed officials who claimed that the once-powerful Iranian army was in shambles — that most of the remaining units were still loyal to the Shah and wouldn’t fight for Khomeini.  The officials were wrong. Iran fiercely opposed the Iraqi invasion in 1980.

Given the prevalent ill-feelings toward Iran generated by the hostage crisis, Americans had mixed feelings regarding the Iraqi invasion and the subsequent Iran-Iraq War.

“It’s a pity they both can’t lose,” Henry Kissinger infamously said of that war. “We wish them both the best of luck,” Israeli prime minister Menachem Begin reportedly quipped upon the war’s onset. One American columnist, musing over which side constituted the lesser evil, even equated it to choosing between cancer and AIDS.

In an editorial for The Los Angeles Times in December 1979, Ernest Conine responded to the initial rumors of the Iraqi invasion by musing if Americans should welcome such a development. Conine listed reasons why Khomeini’s regime was deplorable and a rightful enemy of the United States, but then cautioned his reader against supporting Iraq as a lesser evil.

The disintegration of Iran “is the last thing that Americans should want.”

Were Iranian minorities, such as Kurds and Azeris, to exploit the turmoil caused by an Iraqi invasion to secede. “the Soviet Union, not the West, would gain” Conine wrote, pointing out that the Soviets supported Kurdish and Azeri separatist movements in Iran in the aftermath of World War II.

The Truman administration successfully compelled the Soviets to withdraw, preserving Iran’s unity in the process. Conine argued that were history to repeat itself, Carter “would be in no position to follow Truman’s example,” since Moscow had the “overwhelming preponderance of conventional military power in the area, and the United States is no longer the sole possessor of the atomic bomb, as it was in the late 1940s.”

Conine reached the “uncomfortable conclusion” that while Khomeini constituted “an obnoxious irritant to the United States, the collapse of his authority would be worse as long as there is no alternative leader with the popular following to take his place.”

Late in the Iran-Iraq War, both sides targeted each other’s oil tankers. Iran, which possessed a far superior navy, began mining the Persian Gulf. The U.S. intervened by re-flagging Kuwaiti tankers and escorting them in order to deter Iranian attacks. Operation Earnest Will constituted the largest naval escort mission since World War II.

When in October 1987 one of Iran’s Chinese-made Silkworm missiles struck the reflagged tanker Sea Isle City, injuring 17 sailors, the United States launched Operation Nimble Archer. The U.S. Navy destroyed oil platforms that Iran’s Islamic Revolutionary Guard Corps was using as bases.

In April 1988, the frigate USS Samuel B. Roberts struck an Iranian mine. Ten sailors were injured. The Navy retaliated with Operation Praying Mantis. U.S. ships and planes sank the Iranian frigate Sahand and crippled the frigate Sabalan.

More than 50 Iranians died in the attacks. America’s only loss was a Marine Corps Sea Cobra attack helicopter, which crashed 15 miles southwest of Iran’s Abu Musa Island, killing both crewmembers.

After Operation Praying Mantis, the Iranians eased up their attacks on tanker ships transiting the Persian Gulf.

But tensions remained high. On July 3, 1988, the cruiser USS Vincennesmistakenly shot down Iran Air Flight 655, killing all 290 civilians aboard. Washington insisted it was a case of mistaken identity. Tehran claimed Vincennes intentionally targeted the airliner.

Less than a month later, Khomeini agreed to the U.N. Security Council Resolution 598, which ended the Iran-Iraq War. The frail old ayatollah equated the ceasefire to “drinking a chalice of poison.”

During the U.S. deployment in the Persian Gulf, the commander of the U.S. Pacific Fleet, Adm. James Lyons, strongly advocated a wider war with Iran. Lyon’s proposed Operation Window of Opportunity – which he planned to execute on Aug. 29, 1987 – envisioned U.S. Navy carriers and battleships bombarding Iranian military bases and Silkworm missile sites on Iran’s coast.

The warships would then directly target the Iranian economy by shelling Kharg Island and Iranian ports. Borrowing a page from Zumwalt and Bagley’s proposal nine years earlier, Lyons advocating mining the Iranian ports of Bushehr and Bandar Abbas. He envisioned the operation lasting a mere two days.

Operation Window of Opportunity likely would have inflicted significant losses on Iran, but it wouldn’t necessarily have brought down the regime. Lyon displayed the same overconfidence that plagued Iraqi officials in 1979. They all underestimated the fierceness with which Iranians would resist invasion.