MOSCOW — The authorities in Russia marshaled more than 400 firefighters and 170 emergency workers to extinguish a fire on Friday that had raged for almost a day on the hull of a nuclear submarine in dry dock near the northern port of Murmansk. Seven sailors and two emergency workers were treated for smoke inhalation.

On Thursday, enormous plumes of smoke and flame lighted the sky above the submarine, the 550-foot Yekaterinburg, a Delta IV-class vessel commissioned in 1985. Officials claimed to have brought the fire under control within hours. But on Friday they made clear that the effort had been enormous. Only by partly submerging the vessel were they able to douse the flames on the hull’s rubber coating, which minimizes noise and makes the submarine more difficult for enemies to detect.

The chief of the General Staff of the Russian armed forces, Nikolai Makarov, flew to the snowy port with a team of military investigators, and the story topped the Friday news on Russian television.