At 07:55 on the morning of 18 April 1988, a voice crackled from the destroyer USS Merrill across the VHF band, first in Farsi, then in English: the occupants of the Sassan gas and oil separation platform had five minutes to leave. On the steel decks above the green water of the Persian Gulf, men scrambled for the tugboats tied up alongside. Others ran the opposite way, towards a twin-barrelled 23 mm gun, and trained it on the American destroyer 4,600 metres (5,000 yards) away.

At 08:04, time expired. The Merrill's 127 mm (5-inch) gun flashed. The Iranian 23 mm opened up in reply and was silenced by a direct hit. The one-day war had begun, and by sunset the US Navy would fight its largest surface action since 1945.

The Operations Room reconstructs the one-day war of 18 April 1988, minute by minute.

The road to that morning ran through the Tanker War. Since 1987, under Operation Earnest Will, the US Navy had escorted reflagged Kuwaiti tankers through a Gulf seeded with mines and patrolled by Iranian small craft. On 14 April 1988, the guided-missile frigate USS Samuel B. Roberts, transiting international waters, struck an M-08 contact mine. The blast blew a 4.6 m (15 ft) hole in her hull, flooded the engine room and broke her keel. Her crew fought fire and flooding for hours and saved the ship. Nobody died. It was close.

Divers found more mines nearby. Their serial numbers matched mines seized the previous September from an Iranian minelayer. Washington ordered a proportional response, and planners aboard the command ship USS Coronado in Bahrain worked through the night of 16-17 April. The objectives were precise: neutralise the militarised Sassan and Sirri platforms, and sink the Iranian frigate Sabalan or a suitable substitute.

Three Surface Action Groups

Rear Admiral Anthony Less, commanding the Joint Task Force Middle East, divided his force into three Surface Action Groups. SAG Bravo, with the destroyers Merrill and Lynde McCormick and the amphibious ship Trenton carrying a Marine air-ground task force, took Sassan. SAG Charlie, built around the cruiser USS Wainwright with the frigates Simpson and Bagley and a SEAL platoon, took Sirri. SAG Delta, with Jack Williams, O'Brien and Joseph Strauss, hunted the Sabalan. Overhead waited the aircraft of Carrier Air Wing 11 from USS Enterprise, holding station 220 km (120 nautical miles) outside the Strait of Hormuz.

At Sassan, after the gunfire ceased, Marine AH-1T Sea Cobras suppressed the last resistance and CH-46 and UH-1 helicopters roped a raid force onto the platform. The Marines recovered a wounded survivor, weapons and intelligence, then rigged roughly 680 kg (1,500 lb) of plastic explosive. The remote detonation turned the platform into a torch.

At Sirri, SAG Charlie's shells found a compressed-gas tank and the platform went up without need of the SEALs. So far the operation had run to the minute. Then Iran answered. Boghammar speedboats raced out to strafe targets in the Mubarak oil field, hitting the American-flagged supply ship Willie Tide, the Panamanian-flagged rig Scan Bay and the British tanker York Marine.

Vectored in by a frigate, two A-6E Intruders of attack squadron VA-95 from the Enterprise rolled in on the speedboats with Rockeye cluster bombs, sinking one and driving the rest onto the beach at Abu Musa island. It was the pattern of the day: whatever Iran committed, naval air power met it first. Then the Kaman-class missile boat Joshan came out and pointed her bow at the Wainwright. The cruiser issued a series of warnings, each less diplomatic than the last.

The Joshan's captain replied with his boat's single remaining American-made Harpoon, a leftover from the Shah's arsenal. The missile passed close down the Wainwright's starboard side, seduced by chaff. The reply was clinical: four Standard missiles from the Simpson and one from the Wainwright, all hits. The burning hulk was finished with gunfire. Eleven Iranian sailors died with her.

Minutes later, an Iranian F-4 Phantom pressed towards the group. The Wainwright fired two extended-range Standards; one detonated close aboard, shredding part of a wing. The Phantom's pilot, flying wreckage, somehow recovered the jet at Bandar Abbas.

The Intruders Find Their Frigate

In the afternoon, the British-built frigate Sahand sortied from Bandar Abbas and ran southwest at speed. An A-6E of VA-95, flying surface combat air patrol for the destroyer Joseph Strauss, dropped low for visual identification and was met with anti-aircraft fire and missiles. The Intruders answered with Harpoons and laser-guided Skipper bombs; the Joseph Strauss added a Harpoon of her own, timed with the aircraft in the first coordinated air-and-ship Harpoon attack in combat.

Nearly everything hit. Fires marched down the Sahand's deck until they reached her magazines, and the explosion took her down with 45 of her crew. She remains the largest warship the US Navy has sunk since the Second World War.

Late in the day the Sabalan, the operation's original target, finally came out and fired on the orbiting A-6Es. One Intruder put a 227 kg (500 lb) laser-guided bomb squarely down her funnel. The frigate lay crippled and burning, stern awash. Washington then made a deliberate choice: stop. The Sabalan was allowed a tow home, a signal that the lesson was over. She was repaired and serves in the Iranian navy to this day.

The US Navy did not emerge untouched. After dark, an AH-1T Sea Cobra from the Trenton, flying reconnaissance about 24 km (15 miles) southwest of Abu Musa, went into the sea. Its two Marine aviators were killed. Navy divers recovered them in May; the raised wreck showed no confirmed battle damage. They were the operation's only American dead.

Period news footage of Operation Praying Mantis as it was reported in April 1988.

Iran also fired shore-based Silkworm anti-ship missiles at US ships that day, all of which missed amid decoys and hard manoeuvring. By evening, both sides stood down. In a single day, roughly half of Iran's operational major surface combatants had been sunk or crippled.

The consequences reached beyond the Gulf. Three months later, Iran, exhausted and now certain the United States would fight, accepted the ceasefire that ended the eight-year Iran-Iraq War. The shadow side of the deployment followed within weeks: on 3 July 1988 the cruiser USS Vincennes, sent to the Gulf in the aftermath, shot down Iran Air Flight 655, killing 290 civilians.

Reckoning and Aftermath

Iran took its case to the International Court of Justice, arguing the platform attacks breached the 1955 Treaty of Amity. Fifteen years of litigation ended on 6 November 2003 with a split verdict: Iran's claim for reparations was dismissed, and so was the American counterclaim. But the court did not let the operation pass unremarked — its judgment held that the attacks:

For naval historians, the tactical ledger is less ambiguous. Praying Mantis validated the Harpoon and Standard missiles in combat, proved the value of coordinated air-surface strikes, and demonstrated what a carrier air wing and nine surface combatants could do in eight hours of disciplined escalation. It was measured, it was brief, and it has not been repeated: no navy has fought the US Navy on the surface since.

Sources: U.S. Naval Institute Proceedings, Naval History and Heritage Command, Wikipedia, Military.com