A computer virus forced a US-regulated maritime facility offline for more than 30 hours, the country's coast guard has revealed.
Ransomware interrupted cameras, door-access control systems and critical monitoring systems at the site.
The agency did not reveal the name or the location of the facility targeted by the attack.
Officials said they believed the ransomware was sent in a malicious email link, clicked by an employee.
The US Coast Guard (USCG) issued a security bulletin on 16 December, urging other bases to take measures to prevent further attacks.
"Once the embedded malicious link in the email was clicked by an employee, the ransomware allowed for a threat actor to access significant enterprise information technology (IT) network files, and encrypt them, preventing the facility's access to critical files," it said.
"The virus further burrowed into the industrial control systems that monitor and control cargo transfer and encrypted files critical to process operations."
The BBC has contacted the USCG for more details.
Ransomware attacks were a significant problem during 2019, when several companies and governments were targeted.
The city of New Orleans declared a state of emergency in December after suspicious activity was detected on its network.
Once officials confirmed they were under attack, servers and computers were closed down.
Weeks earlier, Virtual Care Provider, which offers technology services to nursing homes, was hit by a ransomware attack that encrypted patients' health records.
Hackers demanded $14m (£10.6m) to restore access to the hijacked servers.