Retail warehouses tend to have a similar hectic pulse, with workers using forklifts to shuttle items from point A to point B. But UPS’ Velocity warehouse near Louisville, Kentucky, was designed for e-commerce. And it is oddly quiet.

“So we have a little over 700 robots,” said Thomas Stearman, Velocity’s director of industrial engineering, “and the robots work 24 hours a day.”

There are more robots than human workers at the 900,000-square-foot Velocity facility, which opened last winter. This warehouse isn’t just for processing orders and shipping them out. It stores inventory, straight from the manufacturer — though the word “storage” is used lightly here. Most retailers who use this warehouse turn over their inventory every few months. 

“We want to process volume. We don’t want this facility to be a storage facility,” said Stearman. “We want items coming in to be turning.”

One- and two-day shipping, made ubiquitous by Amazon, has put pressure on nearly every other retailer to match it. Meanwhile, the sheer growth of e-commerce — sales have nearly quadrupled over the last decade according to the Census Bureau — has put pressure on retailers and shipping companies to streamline logistics in an effort to shave minutes off the process.

Because UPS’ retail customers at Velocity sell mostly online, they want to move fast to capitalize on trends and get products out quickly. There are five brands stored at this warehouse, with one prominently displayed during the tour.

“There’s one that is our largest customer and one of our fastest growing brands,” said Stearman.

“Marketplace” can’t name the brand because of its agreement with UPS. All we can say is it’s a newish clothing company that focuses on undergarments and loungewear. 

Being newish means the brand is still learning how to be nimble. That’s one of the trickiest parts of shipping logistics. You have to be ready to capitalize on that late-night buyer who needs (or wants) something tomorrow. For next-day delivery via air shipment, Velocity can accept orders until 11 p.m.

Let’s take a second to recognize how totally normal this has become — that you can, phone glowing in the dark, from the comfort of your bed, buy a vegetable spiralizer as late as 10:59 p.m. and be eating zucchini noodles for dinner the very next day.

Here’s what happens after you click “buy” and go to bed: At UPS, it triggers immediate motion. If it’s a popular item, it’s probably already staged in a priority area for stuff that’s expected to sell fast. This requires UPS and its retailers to do a little forecasting.

“Let’s say, if you’re having a sale coming up, well, [we’ll ask] what items are going to be included on that sale, so we’re ready as soon as those orders do hit,” said Stearman.

With one-day shipping, every minute counts. UPS can’t afford to waltz to the deepest depths of its warehouse, one item at a time, and expect to get it across the country in 24 hours. So if a product goes viral and gets more clicks, the stock inches closer to the front of the warehouse, eventually joining a sea of blue crates full of all kinds of trending products. Stearman calls this a dance floor.

“We actually thought about installing a giant disco ball over it,” he said.

This is where the robots live. They look like those Roomba vacuums, but maybe four times the size — big, flat discs scooting under towering stacks of blue bins. The robots whisk them over to packing stations on the other side of the dance floor.

“And we like to call it that because they’ll actually spin as well, and it looks like they’re dancing,” said Stearman.

The robots move non-stop, constantly reprioritizing crates of stuff as UPS’ computers pull in more data about what’s selling. After the orders are picked, humans take over. They’re the ones who pack, tape and label the boxes.

“We’ve got some things to make it easier,” said Stearman. “But it still requires that human touch to be able to really get that out the door for us.”

Out the door of this warehouse isn’t the end of the journey though. Many packages are headed for the airport, just 15 minutes up the highway, for a one-way flight out tonight.