MOSCOW (Reuters) - Russia s defense ministry has sent an oceanographic research ship to the South Atlantic to help with the search for an Argentine submarine which went missing more than a week ago, TASS news agency reported on Thursday. The vessel, called Yantar (Amber), is equipped with two self-propelled deep submergence vehicles allowing it to examine underwater areas up to 6,000 meters (3.75 miles) deep, TASS quoted the Russian military as saying. Dozens of planes and boats are searching for the San Juan submarine. The search entered a  critical phase  on Wednesday as the 44 crew on board could be running low on oxygen, an Argentine navy spokesman said. If the German-built submarine, in service for more than three decades, had sunk or was otherwise unable to rise to the surface since it gave its last location on Nov. 15, it would be using up the last of its seven-day oxygen supply. 