How to Build a Floating Bridge in 12 Minutes

As the County Fire tore through Northern California this summer well on its way to burning 90,000 acres in Napa and Yolo Counties, Harley Ramirez got a call. The 132nd Multirole Bridge Company of the California National Guard was heading toward the blaze, and Sergeant First Class Ramirez was being put in charge. His team’s mission: help the California Department of Forestry and Fire
Protection, better known as Cal Fire, get its people, equipment, and supplies to the front line by building a floating bridge across a river in Cache Creek Regional Park. As quickly as possible.
Before long, Ramirez was watching a truck called a common bridge transport slide a folded up pile of metal into the river, where it unfurled itself in two splashy steps, a piece of origami reverting to its original state. The suddenly flat slab of aluminum floated on the surface, held in place by ropes gripped fiercely by Ramirez’s soldiers. This was the first piece of the improved ribbon bridge the 132nd had come to here to build, a Lego-like thing that would save California’s firefighters vital time in their efforts to contain the County Fire, and provide them an escape route should they have to fall back.

The 132nd is just one of many military units around the country and planet trained to install this sort of floating, temporary bridge, meant to last a few weeks and move supplies and people when war or natural disaster nix standard engineering solutions. This variety of bridge—designed by General Dynamics European Land Systems—has bridged the Tigris and Euphrates Rivers as American soldiers invaded Iraq in 2003, helped workers get cranes and oil booms into the Gulf of Mexico to contain the 2010 Deepwater Horizon oil spill, and stretched across Poland’s Vistula River during NATO’s training exercise, Exercise Anakonda, in 2016. And as Hurricane Florence continues to flood the mid-Atlantic, they’re being readied to move emergency personnel and relief supplies into the river-surrounded town of Georgetown, South Carolina.

Any improved ribbon bridge is made up of two types of bays, essentially big floating rectangles. The ramp bays, which have one sloped side, will connect to each shore. The interior bays go in between them; their number depends on how long a bridge you’re making. Each is 22 feet long, weighs about 13,000 pounds, is made of aluminum, and floats the same way a pontoon does. Usually, the crew launches one of the ramps into the water first, using that common bridge transport, which backs up to the water and uses a crane arm to slide the payload off its flatbed. They usually angle this first piece of equipment upstream, so it’s out of the way as they drop the other bays drop into the water.

For easier transport on land, each bay is folded up like a ‘W’. Once on the water, it unfurls with a splash, and crew members in bridge erection boats—essentially high performance tugs—nudge it into position. Once two bays are lined up, the soldiers dash over to lock them in place. They start by using supersized hex wrenches to drop heavy duty pins, 2 inches round, into a set of interlocking loops. Then they deploy the “dog bones,” the spring-loaded dumbbell-shaped locks that span the two bays, fitting into a special groove. Meanwhile, the landlubbing crew members use cables to anchor the ramps, usually sinking them into the ground or tying them to trees. And that’s about it.

Uninstalling an improved ribbon bridge is about a simple as setting it up. Unlock the bays, push them to shore, and use that crane-wielding boat to winch them back to dry land, in the process folding them back into that W-shape. Then put them away until the next time someone needs a bridge over troubling waters.

“It’s a hasty way of making a bridge,” says First Lieutenant Colin Francis, formerly of the 132nd, who took part in the Cache Creek build. An effective one, too. An improved ribbon bridge can support 70 tons or more—enough to carry an M1 Abrams tank—and is solid enough that you’ve got to drive across in a semi-truck to feel it move in the water.

In ideal conditions, a trained crew can build a 100-foot bridge (that’s with two ramp bays and three interior bays) in about 12 minutes. “Ideal” here means calm water that’s at least two feet deep, with a shallow bank and plenty of room to maneuver. But war zones and natural disaster areas are not what you’d call ideal conditions, so the 132nd Multirole Bridge Company trains for as many situations as possible. Not that they can prepare for everything.

Even before dropping that first bay into the river, Ramirez knew his team had a problem. They were working around an existing bridge (built in 1930 and no longer rated to support the heavy duty equipment Cal Fire needed to move), and didn’t have the space to deploy the bridge erection boats that maneuver the bays into place. The crew had started by hanging onto the bay with ropes, but in an unhelpfully swift current, they were losing the tug of war.

Then they saw the bulldozer Cal Fire had brought to the crossing, and changed the plan. The soldiers tied the ropes onto the machine and stepped back. Then the contractor who’d come up to drive the thing hopped in the cab and carefully moved forward and back, easing the bay—and the next four—into just the right spot. No bridge erection boats, no problem.

“We have no training to bulldoze a bridge into place,” Francis says. But they are trained for improvisation and flexibility—to do whatever it takes to build what needs building. The unusually complex build took them just a few hours. Hardly a record for the 132nd, but fast enough to let CalFire get its equipment and manpower where they had to be that very night.