If Australia is to choose the Japanese contender for their future submarine then it should be because it’s the best fit for our ongoing strategic requirements, fully meets project criteria, and is the most economically viable from now until the end of the 2060’s. This decision shouldn’t be a ‘captain’s pick.’

The Soryu-class (‘Blue Dragon’) submarine provides the capability the Japanese Maritime Self-Defense Force’s needs. But the current Soryu-class won’t meet Australia’s requirements. We will need Soryu Mark Two (Goryu? ‘Australian Dragon’) as a completely new design, which will have cost, performance and schedule risks. It won’t be a Military off-the-Shelf (MOTS) acquisition, as some seem to think. Similarly, the hull can’t be built in Japan and fully fitted out in Australia.

The Soryu fleet includes six commissioned vessels, which have a surface displacement of 3,480 tons (compared with the Collins-class 3,100 tons) and are 84 meters long. A further five are in various stages of construction.  There’s a continuous build program, with both Mitsubishi Heavy Industries (MHI) and Kawasaki Heavy Industries (KHI) involved and alternating the start of each new vessel.

There are a number of major changes required for Mark Two in evolving a design to meet RAN’s requirements. This is no simple matter and presumably the CEP will establish how this could be accomplished.

The Soryu-class are currently operated and maintained for a service life of 20 years. Australia will want 30 years. Welding techniques, the steel used, corrosion control and number of compression/decompression cycles from deep dives all affect service life. So too do the maintenance and upgrade arrangements—Japan will need to create a new upkeep plan for Mark Two.

Australia needs a greater range than the current Soryu. The Collins-class has a range of 11,500 nautical miles at 10 knots surfaced and 9,000 nautical miles snorkeling just sub-surface at the same speed. Fully submerged it has a range of 480 nautical miles at 4 knots, when running on lead-acid batteries.  Soryu has a surface range of 6,100 nautical miles at 6.5 knots, faster underwater. This will need to be increased in Mark Two by more fuel-efficient engines and extra bulk fuel storage—perhaps by filling some water ballast space with fuel, to get longer range.

Remaining silently at depth for periods of up to 35 days, while travelling slowly for approximately 4,000 nautical miles in the patrol area, will be important for Australia’s next submarines. Although not specified explicitly in the CEP criteria, Australia needs an excellent Air Independent Propulsion (AIP) system and specialist batteries to give the required endurance.

The Japanese have obviously made significant progress with Lithium ion batteries (LiBs) to the point where they are proposing that the final two Soryus being constructed in Japan about 2020 abandon their Stirling AIP engines and have only LiBs. LiBs are much more energy dense, providing up to four times as much power in the same space as occupied by classic lead accumulators. If this happens, this is a major technology advance as currently no commissioned diesel-electric submarine in the world has gone to sea with LiBs.

Diesel engine-driven battery charging technology needs to adapt to the new requirements—the need for much more electrical power for faster charging possible with LiBs. Currently, Soryus have two chargers, while Collins-class have three. This has significant implications for detectable snorkel depth battery charging time, which means that Soryus currently may have the higher indiscretion ratio. Mark Two must do much better.

Soryu Mark Two will be offered with a permanent magnet synchronous electric motor, with the advantage that brings of high torque at low revolutions, keeping propeller noise to a minimum and avoiding the need for a gearbox.

The Soryu-class have a Hitachi command and control system, while Australia wants the U.S. AN-BYG-1 installed, a first for Japan. In terms of weaponry, the Soryus can launch Type 89 torpedoes, Harpoon missiles, and mines. Australia wants Mark 48 Mod 7 CBASS torpedoes, mines and probably the same UGM-84C Sub-Harpoon missiles as fitted in Collins Class. There will also be issues over which type of sonars should be fitted.

Cultural differences between the Japanese and Australian defense industries will be challenging. If they’re lining up an Australian-based partner to help them deal with the serious issues ahead, there’s been no public disclosure as yet.

The best chance for a successful Mark Two design and construction program with MHI and KHI, as Australia’s international partners, appears to be a hybrid build. The first one or two submarines would be built completely in Kobe, with heavy involvement by Australian designers and shipyard workers there, before construction shifts to Adelaide for the remaining vessels in the project.

In the political arena, given that China is Australia’s number one trading partner, what would be the impact of teaming with Japan and the U.S. in what will be seen by China as a strategic coalition to contain their naval expansion? Neither French nor German CEP contenders have this problem.

This piece first appeared in ASPI’s The Strategist here.