Indonesian authorities have said the submarine has only hours of oxygen left and needs to be rescued before that. The lives of at least 53 crew members are at stake.
The submarine lost contact after asking for permission to dive during live torpedo exercises off the coast of Bali on Wednesday.
Officials have suggested that the submarine, KRI Nanggala 402, disappeared because of damage to its fuel tank.
John Kirby, a Pentagon spokesperson, told the media that the US was deeply saddened by the turn of events.
“Our thoughts are with the Indonesian sailors and their families. At the invitation of the Indonesian government, we are sending airborne assets to assist in the search for the missing submarine,” he said.
Germany, France and Australia have also offered help to the Indonesian government in the hunt for the vessel, and Malaysia and Singapore have sent ships to the area where the military suspects the submarine went missing.
At least 400 people, six warships and a helicopter have been frantically searching for it since it disappeared.
In a press release, Australia announced: “HMA ships Ballarat and Sirius, both presently at sea on separate regional deployments, are making best speed for the search area.”
Achmad Riad, an Indonesian military spokesperson, told the media on Thursday that they had found some signs of an object at a depth of between 50 and 100 metres.
The military called in ships and began using sonar tracking equipment in an attempt to find KRI Nanggala 402.
Mr Riad said: “We’ve only got until 0300 tomorrow [Saturday] so we’re maximising all of our efforts today.”
KRI Nanggala is a 1970s German-built vessel and is the only submarine operated by Indonesia to have gone missing.
On Thursday, Mr Kirby said: “Defence Secretary Lloyd Austin will speak with his Indonesian counterpart, Defence Minister Prabowo Subianto, Friday morning to discuss what else the US can do to assist the search.”
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