During the Vietnam War, American commandos developed an insertion and extraction method for operations in the jungle that is still used by today’s special operators. The Special Patrol Insertion/Extraction (SPIE) system is designed for small special operations teams that operate in areas where an enemy presence or the terrain prevents helicopters from landing.

The SPIE technique hasn’t been used operationally for decades, in part because U.S. air superiority and lackluster enemy anti-aircraft capabilities have meant it wasn’t needed.

But as the U.S. military gears up for great-power competition against near-peer adversaries, like China and Russia, the SPIE technique becomes relevant again, especially in a potential conflict in the Pacific.

Warriors of the Jungle

The SPIE system can be traced to the rope insertion and extraction techniques of the Vietnam War. It was the innocuous-sounding Military Assistance Command Vietnam-Studies and Observations Group (MACV-SOG) that invented and used the method.

A highly classified unit, SOG took the fight to the North Vietnamese Army and Vietcong, conducting cross-border operations into Laos, Cambodia, and North Vietnam — where U.S. troops officially shouldn’t have been.

Composed of Green Berets, Navy SEALs, Recon Marines, Air Commandos, and indigenous forces, SOG tried to stop the onslaught from the North and give South Vietnam some breathing space.

SOG’s classified operations mainly took place in rough and inaccessible jungle, where the NVA had built the infamous Ho Chi Minh trail complex, over which flowed supplies to its forces in South Vietnam. The terrain restricted operations and often forced SOG teams to create their own landing zones by either detonating explosives or by requesting B-52 bombing runs to create craters where helicopters could land.

But landing wasn’t always an option. Secrecy was paramount for mission success. After all, SOG patrols of six to 14 men didn’t have a chance of survival against hundreds or thousands of NVA in an open battle.

With so few landing zones available in the jungle, and with the NVA always trying to monitor them, SOG operators came up with different techniques that didn’t require landing.

Ropes Away

At the time, the SPIE terminology didn’t exist, and operators simply used the term “ropes” to refer to methods such as the STABO Extraction Harness, McGuire Rig, and “Swiss Seat.”

The STABO Extraction Harness, or STABO rig, was one of the most used. Designed for quick infiltration into and exfiltration from the jungle, the STABO rig was a mandatory piece of equipment for every recon member. It was worn throughout the mission since recon team members didn’t know if or when they would be compromised, which would often mean a frantic race to escape from superior forces.

During an extraction by ropes, the helicopter crew chief would throw ropes, with a sandbag tied to one end, down from a hovering helicopter. SOG commandos would hook the ropes to links on their uniforms. The helicopter would then rise straight up to clear the jungle before flying away.

Throughout the Vietnam War, ropes methods saved several lives, and their use sometimes seemed straight out of a movie.

In June 1967, a reinforced SOG company composed of Green Berets and local troops entered Laos to conduct a battle-damage assessment after an airstrike on a North Vietnamese headquarters hub along the Ho Chi Minh trail complex.

The roughly 100-man “Hatchet Force” came upon a strong NVA force, and a fierce battle ensued. The American commandos and their local allies were surrounded and pinned down, but their firepower saved them from being overrun.

The NVA shot down several fixed-wing and rotary-wing aircraft that tried to exfiltrate or support the battered SOG company. Eventually, some choppers were able to come in and exfiltrate members of the force.

During one of those trips, a Marine Corps CH-46 Sea Stallion was shot down close to the Hatchet Force’s perimeter. Somehow, Sgt. First Class Charles Wilklow survived the crash, though he was badly wounded.

The NVA captured him but, seeing his wounds, thought he only had a few hours to live. They tied him down and used him as bait for a rescue operation. Considering the certain failure of a rescue mission, SOG headquarters didn’t take the bait.

After four days, Wilklow was still alive, despite his grievous wounds. Yet the NVA didn’t guard him, believing he wouldn’t survive. Wilklow managed to free himself and crawl into the jungle at night.

The next day, a SOG forward air controller spotted an almost-dead Wilklow. He was soon extracted by ropes — despite his ordeal, he was still wearing his STABO rig.

Moving Parts

As tensions with China rise, and with a conflict in Southeast or East Asia a growing prospect, the SPIE method is increasingly relevant, but it remains risky and inconvenient.

“[SPIE] operations are pretty dangerous, with lots of moving parts that can potentially go wrong,” a Marine Raider told Insider. “You have to watch as you exit the aircraft mid-air, and more so if you’re the first man out because you’ve got five, six, sometimes seven guys right behind you while the pilots are trying to hold position midair. You also have to account for the rotor wash in water and desert ops. You can’t see much while landing because of the sea spray or dust in the air.”

Since the SPIE technique can be used for both land and water operations, it provides special operations units with more choices when planning ops in the Pacific theater.

For example, the SPIE technique can be used to extract Navy SEALs conducting special reconnaissance along the Chinese coast or a Special Forces detachment doing unconventional warfare in support of local forces on China’s borders.

This article was written by Stavros Atlamazoglou and originally published on Insider.