Three C-17 aircraft are expected to depart Dover Air Force Base Friday with watercraft and underwater search and rescue gear to assist with ongoing efforts to locate the submarine before the vessel runs out of oxygen.
The equipment will help in the search and rescue efforts and if necessary, assist in a recovery mission.
“We are deeply saddened by the news of Indonesia’s lost submarine, and our thoughts are with the Indonesian sailors and their families,” Pentagon press secretary John Kirby tweeted Thursday. “At the invitation of the Indonesian government, we are sending airborne assets to assist in the search for the missing submarine.”
The KRI Nanggala-402, a German-made submarine, lost contact during a military exercise local time Wednesday in the Bali Strait, a stretch of water between the islands of Java and Bali that connects to the Indian Ocean and Bali Sea, according to the Indonesian Ministry of Defense.
Indonesian search teams had narrowed down the search area Friday, after detecting an object likely to have come from the submarine, but are running short on time.
Adm. Yudo Margono, chief of staff of the Indonesian Navy, said at a news conference Thursday that the vessel has sufficient oxygen for all the submariners until Saturday at 3 a.m. local time.
The US assets will join a sprawling search effort. Three submarines, five airplanes and 21 warships have been deployed to help search for the missing sub, Margono said. Assets from Singapore and Malaysia are also en route to assist.
Defense Secretary Lloyd Austin spoke with his Indonesian counterpart, Defense Minister Prabowo Subianto, Friday morning to “express his heartfelt concern” over the missing submarine, a readout from Kirby said.
The two discussed the “recent deployment of a P-8 Poseidon aircraft to aid the search,” and “offered to provide additional assistance,” the readout said.
The Indonesian military suspects that an oil spill seen in aerial surveillance near the dive point on Wednesday came from the craft. Margono said the Navy also found one object at the depth of 50-100 meters (approximately 164-328 feet) that was magnetic, meaning it likely came from the submarine.
Margono said there are two possibilities to explain the oil spill spotted on the surface: the submarine tank could be leaking because it dove too deep, or the submarine released fluid on board in an attempt to rise to the surface.
Indonesia has been seeking to upgrade its defense capabilities, but some of its equipment still in service is old and there have been deadly accidents in recent years, in particular involving aging military transport planes.
This story has been updated with additional reporting.
CNN’s Masrur Jamaluddin and Veronica Stracqualursi contributed to this report.