Russia's only aircraft carrier, the Admiral Kuznetsov, is one of the five worst carriers in the world, according to The National Interest.
In October 2016, the Kuznetsov was sailing to Syria through the English Channel on a combat deployment when it was spotted belching thick clouds of black smoke.
"The main problem with the ship is that is has a very problematic propulsion system," Dmitry Gorenburg, a senior research scientist at the Center for Naval Analyses, previously told Business Insider. "It's just unreliable."
Before it was sent back to the yards for repairs, the Kuznetsov was always accompanied by a special tugboat in case it broke down, and the plumbing was said to be so bad that most of its toilets didn't work.
It's being refitted at Russia's 35th Ship Repairing Yard in Murmansk and won't be ready to return until 2021.