UNITED NEWS INTERNATIONAL (UNI) — India’s first nuclear-powered ballistic missile submarine has been sidelined for nearly a year after its propulsion compartment was left open and it flooded with seawater.

The $2.9 billion INS Arihant has been out of commission since last February after “human error” caused major water damage to the submarine’s propulsion chamber.

According to a Jan. 8 report by The Hindu, the nuclear submarine was docked at the harbor when somebody accidentally left the hatch open, causing water to flood into the rear side of the vessel.

The sub, which reportedly nearly sank thanks to the mistake, has been undergoing repairs since then.

Construction on the Arihant, India’s first ballistic missile submarine, began in 2009. The ship was commissioned into the Indian Navy seven years later in October 2016.