"An aerial surveillance by a helicopter at 7 a.m. recorded the oil spill around the early position of the submarine's dive," the ministry's secretary general stated in a press statement here on Wednesday evening.
The Defence Ministry keeps monitoring the search efforts to locate the submarine carrying 53 sailors that lost contact after receiving a clearance for diving at about 3 a.m. on Wednesday.
The search mission is continued by deploying Indonesian naval ship KRI Rigel and KRI Rengat, equipped with side scan sonar devices.
The Indonesian Navy has also sent a distressed submarine to the International Submarine Escape and Rescue Liaison Officer (ISMERLO), the Defence Ministry revealed.
Navies of several countries, including Australia, India, and Singapore, have responded and offered a help for searching the missing submarine, the ministry said.
Indonesia has sought help from Singapore and Australia in the search for its submarine KRI Nanggala-402.
"We have had good cooperation with Singapore and Australia in the search and handling of training accidents," Military Commander Air Chief Marshal Hadi Tjahjanto said.
Besides appealing to the two friendly countries for help, the Indonesian Navy has pulled in all ships equipped with underwater devices for the search and rescue mission, he informed.
Contact with German-made KRI Nanggala-402, which was carrying 53 sailors on board, was lost while it was preparing for a torpedo drill in Bali waters.
"The last contact was made at 4:30 a.m. local time. There was no more contact when the torpedo drill was to be conducted," Tjahjanto informed.
Tjahjanto is currently in Bali on a working visit along with National Police chief, Gen.Listyo Sigit Prabowo.
They were scheduled to observe the submarine's torpedo drill on Thursday, following which Tjahjanto was to offer a brevet to the national police chief.
The missing 209/1300-type submarine was built in Germany's Howaldtswerke-Deutsche Werft in 1977, and was officially inducted into the navy in 1981.
Its propulsion system uses a Siemens low-speed diesel electric motor, connected directly to the propeller shaft, which generates about five thousand shaft horsepower (shp).
The electrical power is stored in batteries, which make up 25 percent of the weight of the vessel, according to the navy. Four MTU diesel supercharged engines are responsible for generating electricity in the vessel.