Rescuers are racing to find a missing Indonesian submarine, as authorities say the 53 sailors onboard only have enough oxygen to last until Saturday (April 25).Neighboring countries have stepped in to help detect any signs of the KRI Nanggala-402, which lost contact on Wednesday (April 21). Australia's foreign minister said the country would "help in any way we can", while Singapore has deployed a submarine rescue vessel to aid the search, the city-state's defense minister has said. Malaysia was also sending a ship.Here's Indonesian president, Joko Widodo. "I have ordered the military chief, navy chief of staff, and the search and rescue agency to use all possible efforts and capabilities to carry out an 'optimal' search and rescue operation. The main priority is the safety of the 53 crew members."An aerial search discovered an oil spill near the submarine's dive location, which the navy say could indicate damage to the vessel or be a signal from the crew.Two navy vessels with sonar capability have been deployed to assist the mission.Indonesia's naval chief of staff Yudo Margono said the submarine was in good condition, and had been cleared for use. The defense ministry say the 1,395-tonne vessel joined the Indonesian fleet in 1981.It underwent a two-year refit in South Korea that was completed in 2012.Earlier, a navy spokesman told national television that the submarine could sustain a depth of up to 1,640 feet.Although the seas in the area are shallower than in other parts of the archipelago, they can still reach depths of almost 5,000 feet.Indonesia only has a fleet of five submarines, and has been seeking to modernize its defense capabilities.But some of its equipment is old and there have been fatal accidents in recent years.