Second Hand Submarines No Solution for Australia

My thanks to Anonymous, who on December 24, 2021, raised the Japanese confidentiality problem (which would include Japan's special HY-156 pressure hull steel) of Japan selling its submarines. This is in the context of Bradley Perrett's December 23 suggestion that Australia could relatively quickly and simply buy second-hand Japanese Oyashio class submarines to resolve some of Australia's incredibly complex submarine problems. 

Bradley suggestion, while attractive to some, falls down for many reasons, including:

-  the Oyashio subs (commissioned 1998 - 2008) are as old as the Collins (commissioned 1998 - 2003)

-  Japan is undertaking mid-life upgrades to its newest 7 Oyashios so that they can remain effective operational subs for the Japanese Navy. They are being upgraded at great expense rather than simply depreciating with age. That being the case Japan will not part with its Oyashios.

- the Japanese military and political establishment lost face when the Australian purchase of Japanese subs, promised by Prime Minister (PM) Abbott in 2014, was ignored by PM  Turnbull, when Australia chose France in 2016. This means Japan is unlikely to risk being played by Australia again.   

- the suggestion that Australian owned Oyashios could be overhauled in Japan would be unacceptable for Australian strategic, logistical, union and other political reasons.

-  Japan's subs are too short range for Australia's environment. Japan's longest patrol distance is only from southern Japan to the the northern tip of the Philippines. While Japan does not publish the range of its Oyashios they actually have a range of 6,000nm thus rendering them useless for most Australian mission needs. 

-  Collins have and need twice the range at 11,500nm. This range is for the 6,000nm to transit to-from their operational areas north of Australia. Then at least 5,500nm to operate on station.

-  if Oyashios were used in Australian service they would need to be heavily and expensively modified to take the US-Australian electronics suites used on the Collins and which is to be  used on Australia's future nuclear subs. That includes the AN/BYG-1 combat system of sensors, databases, workstations and weapons (especially the Mark 48 torpedo).

-  Bradley's suggestion "The more submarines in service, even if they are diesel powered, the easier it will be to create crews" doesn't follow. Australia finding twice as many crews to operate not one but two types of conventional submarines while simultaneously training other Australian crews to operate the future nuclear subs would dilute limited defence resources.

A more viable solution remains the Collins' mid-life overhaul aka life of type extension (LOTE). The biggest limiter on submarine lives is metal fatigue of the pressure hull caused by the number of immersion cycles. Each time a submarine dives its pressure hull contracts and then it expands as it returns to the surface. The Collins' pressure hulls have spent more than their years would suggest out of the water due to long diesel overhaul periods. So they have a lot of life left in them. If the LOTE includes replacing the Collins main defect, the overhaul-intensive Hedemora diesels, with the world's most common submarine diesels (built by MTU) then the Collins could well operate efficiently out to 2040. Note that Australia recognised the value of MTU diesels in 2019.