For the latest specifically on the Soryu see:
- Australia's Future Submarine likely to be Japan's Soryu, outsiders is Germany dated September 8, 2014, and earlier
- Increasing Australian Interest in Japan's Soryu Submarine dated June 1, 2014, and
The Sōryūs have a very large displacement for a diesel-electric sub (2,900 tonnes surfaced and 4,200 tonnes submerged). This compares to the Collins (3,050 tonnes surfaced and 3,350 tonnes submerged) http://en.wikipedia.org/wiki/Collins-class_submarine.
Significantly the Soryu carries a higher weapons payload than the Collins which is an important endurance-operational advantage. The Soryu carries 30 "reloads" (torpedos/Harpoon missiles) compared to 22 for the Collins.
The Soryus are fitted with air-independent propulsion (AIP) based on Kockums Stirling engines license-built by Kawasaki Heavy Industries . The diesel-electric range surfaced may be around 11,000 km with AIP range 1,000+ km. Range (how much on diesel, batteries and AIP?) is one of the most complex issues involving submarines. The Soryu is mainly heavier than the Oyashio's tonnage (2,750 tonnes surfaced and 4,000 tonnes submerged) due to the addition of the AIP.
See also Kawasaki is involved in producing "more than 80" Japanese submarines http://www.khi.co.jp/english/ship/product/submarine/index.html .
Possibilities of technology Soryu transfer from Japan to Australia particularly concerning the propulsion system were described at Japanese Media Now Openly Talking about Japan-Australia Soryu Deal, February 17, 2013 http://asw.newpacificinstitute.org/?p=11560 .
According to http://www.globalsecurity.org/military/world/japan/2900ton.htm: The Soryu features higher automation (particularly in combat systems) and computer-aided X control planes. The X rudder configuration was first developed by Kockums for the Gotland. The X rudder provides the submarine with greater manoeuvrability and also enables operation close to the seabed. As with most modern submarines the Soryu's hull is clad in anechoic coating (to reduce sonar and other forms of detection) and the interior features sound isolation of loud components. The hull is HY-80 alloy (the same as the USN's Los Angeles class SSN) steel.
Japanese subs have a short service life averaging around 20 years compared to 30 years for most SSKs. It is not known whether the Soryu's propulsion system is designed for a less than 30 year service life.
Japan's lack of experience in exporting submarines or other major weapons systems has many political, legal and technical support implications that Australia would need to resolve and feel confident about. Japan's US-2 amphibious aircraft sale to India provides a limited test of Japan's ability to export arms. A Collins II deal might test Japanese companies ability to integrate their product in simultaneous negotiations with Australian, European and US submarine arms companies.
But then again the political, strategic, and repair-maintenance advantages of choosing a propulsion design from an Asia-Pacific ally like Japan must be factored in. Such advantages would not be present if Australia purchased propulsion systems from more distant Germany (HDW), Spain (Navantia), Sweden (Kockums) or France (DCNS). Japan and Australia also have a joint interest in containing China.
One confidence booster is that the main builders and presumably sellers of the Soryu, which are Mitsubishi and Kawasaki, are highly export and customer support orientated. Such confidence would assume that the corporate culture in Mitsubishi's and Kawasaki's defence product divisions are similar or the same as their civilian product divisions.
As the Soryu combines many of the best European technological features and in a design near to SEA 1000's Asia-Pacific endurance requirements the Soryu Class propulsion system looks a promising option for Australia.