Japan has assured Australia it will share its most secret stealth technology if it wins a contract to design and build Canberra's next generation of submarines, a report said Monday.

Three international bidders are competing for the project worth up to Aus$50 billion (US$36 billion) to replace Australia's current diesel and electric-powered Collins Class submarines which are set to be retired from about 2026.

The tender process is now closed with submissions received from DCNS of France, Germany's TKMS and the Japanese government.

Besides matching the range and endurance of the Collins Class, the new generation of subs are expected to offer superior sensor performance and stealth capabilities.

Japan's Deputy Defence Minister Kenji Wakamiya said Tokyo ordinarily only shared details of its Soryu class submarine with the United States, but Australia was also considered a deeply trusted ally.

"It is of major importance to us that we will be sharing this secret technology with Australia," he told The Australian newspaper in comments published Monday.

Wakamiya added that Tokyo's willingness to do this demonstrated the importance it placed on maintaining regional security.

"Please also recognise that this decision was based on Japan seeing Australia as a very important partner," he said.

"And I believe that a joint project to build the new submarine would contribute greatly to maritime safety in this region."

Late last year Japanese Defence Minister Gen Nakatani echoed similar sentiments that picking Tokyo could help ensure maritime security in the Asia-Pacific.

He was alluding to the importance of allies such as the US, Japan and Australia working together in the face of China's growing military might.

For Australia, cooperating with Japan -- whose Soryu is widely seen as the best submarine of its type -- risks angering its biggest trading partner China.

According to the report, Japan is offering to build a new Soryu with its hull extended six to eight metres (20 to 26 feet) to carry more batteries and fuel to take account of the massive distances the Australian navy travels.

The tender process has been politically sensitive, with Canberra keen to maximise Australian industry involvement and jobs. There are fears that any off-the-shelf purchase could kill off the domestic shipbuilding industry.

Japan, France and Germany all have said they will build a large part or all of their submarines in Australia with the competitive evaluation process expected to take 10 months.

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