A flooded subway entrance stopped Brooklyn commuters in their tracks yesterday. For four hours on Wednesday, the staircase leading down to Broadway Station in Williamsburg was blocked off and completely submerged. The sight was even stranger since it hadn’t rained in New York City that day.

It turns out that the flooding was intentional; the city’s Metropolitan Transit Authority was testing one of the gadgets it has put in place to protect the subway system from a future super storm. In the case of a real disaster, a “flex gate” seals off the entrance to the station and can hold back up to 14 feet of water. The MTA says that it was checking to make sure that a new gate at the Broadway Station was installed correctly; it passed the test.

Kaye Blegvad stumbled across the spectacle on her commute, and tweeted a photo and and asked the MTA to explain itself. “At first I thought the whole subway might be flooded, but everyone around seemed pretty unbothered in typical NYer fashion,” Blegvad wrote to The Verge in an email. “It just looked very surreal and weird.” She soon discovered that other entrances to the station were open and dry, and was able to hop on a train.

In response to Blegvad, the MTA quipped, “We’re pivoting to submarines.” Then in another tweet, it explained its reasons for the “test flood,” adding, “We’re doing this because climate change is real.”

Climate change is expected to bring heavier rainfall, higher sea levels, and more frequent and intense storms to New York City. When Hurricane Sandy pummeled through New York City in 2012, floodwaters inundated several stations from track to ceiling with corrosive salt water. Two Long Island Rail Road tubes between Manhattan and Queens were submerged. Tunnels, bridges, subway yards, and bus depots were damaged.

So after Sandy, the Big Apple launched an initiative to make its public transportation more resilient. Over the past seven years, it has rolled out upgrades in stations and tunnels to prevent future flooding from inflicting the same destruction. That includes the flexible stairwell cover tested yesterday, and 64* others like it across the city. The “flex gate” is made of Kevlar that a single person can put in place in just minutes. The device was designed by the same company that created spacesuits for NASA’s Apollo astronauts, ILC Dover.

All in all, the MTA has installed equipment — including other gadgets like 3,000-pound submarine-like doors and portable vent covers — at roughly 3,500 points where water might enter the subway system.

The work of retrofitting New York’s subways for a changing climate is ongoing, and the MTA tells The Verge there will be more “flood tests” like the one that took place yesterday. In an update on the resiliency initiative released on the seventh anniversary of Hurricane Sandy on October 29th, MTA chairman and CEO Patrick Foye said in a statement, “We have a responsibility to the entire region to make sure we finish the job, and we will do so.”

*Correction 11/21: A previous version of this article stated that there are 67 additional “flex gates” throughout the city aside from the gate at Broadway Station. When The Verge asked the MTA how many gates were installed in the city, the MTA initially said in an email that there were 68. The MTA later clarified that it has so far installed 65 and plans to install three more.