Fort Bragg, the US Army’s largest base issued an apology earlier this week following an unannounced exercise to see what would happen in the event of a cyberattack. The base lost power for 12 hours on Wednesday and Thursday, and caused some confusion and concern on the base.

Army officials told the Charlotte Observer that the exercise was designed to “identify shortcomings in our infrastructure, operations and security,” and wasn’t announced to the public in order to “replicate likely real-world reactions by everyone directly associated with the installation.”

Power on the base went out around 10PM EST on Wednesday, and returned over the course of Thursday afternoon. Residents on the post reported some of the issues that the blackout caused on Facebook and Twitter, from traffic issues caused when traffic lights went out to getting official documents updated, as well as their overall confusion about the lack of updates from official sources. Others took the situation in stride.

@FtBraggNC blackout? No power? No worries. Here’s how we get to work. #LetsGo day or night. pic.twitter.com/KJmLSrIHtM — 2nd Brigade, 82nd Airborne Division (@2BCT_FALCONS) April 25, 2019

On its Facebook page, the US Army apologized for causing concern, and explained that it was part of a required test for the base to “determine the readiness and resiliency of the installation in a real-world scenario. With that said, our objectives have been met and as many of you know, everything is back to normal.”

In recent years, officials have become increasingly concerned that the country’s power grid and infrastructure is vulnerable to cyberattacks. Such attacks aren’t unheard of: a couple of years ago, Ukrainian power plants and airports experienced such attacks, and US officials have said that they’ve detected Russian-linked actors targeting US facilities.

With more than 50,000 soldiers stationed there, Fort Bragg is the largest military base in the world, and is home to the US’s XVIII Airborne Corps and Special Operations Command. It’s worth noting that Army bases like Fort Bragg are more than just training facilities for the military — they’re full-fledged towns, with housing for soldiers and their families, stores, restaurants, hotels, museums, post offices, and more. As of 2000, the base was home to nearly 30,000 other residents. Given the base’s size, a real attack against its infrastructure could cause significant problems — especially if timed to interfere with something like a large deployment or exercise.

Unfortunately, there’s only so much planners can do in order to actually see what happens during such an incident, and deliberately putting the base through a live test should provide the base with some new data learn from moving forward.