Rescue teams in Indonesia have stepped up their search for a submarine and its 53-person crew that went missing more than 24 hours ago. According to an internal Indonesian Navy report seen by Al Jazeera, a distress signal was sent by the Indonesian authorities to the International Submarine Escape and Rescue Liaison Office (ISMERLO) on Wednesday afternoon. ISMERLO coordinates international submarine search and rescue operations and the Singapore Navy and the Australian Navy responded to the distress signal, according to the report. “Singapore has a specially built submarine rescue ship along with a Deep-Submergence Rescue Vessel (DSVR) to perform complex rescue operations. Indonesia has no such equivalent capability,” Dr. Collin Koh, a Research Fellow at RSIS who specialises in naval affairs and maritime security, told Al Jazeera. The two countries signed a submarine rescue pact in 2012, and Singapore’s Defence Minister Ng Eng Hen wrote on social media on Thursday that the vessel – MV Swift Rescue – had been dispatched “as fast as she could get ready”.