As the Abbott Government has already chosen Japan's Soryu even the most senior defence officials are limited in what they can say to Australian Senate Committees. To provide full and accurate answer to Senators risks being considered disloyal to Australia's (current) Prime Minister Abbott's decision - increasingly know as the Captain's Pick. Put another way accurate information should be avoided if it potentially provides ammunition for politicians who oppose the Japan decision.
Australia has stated a preference for the US submarine AN/BYG-1 combat system (made for US weapons) and US Admiral Thomas is enthusiastic that Australia buy the Soryu. The implication from this is that the US is more likely to supply its combat system with associated US weapons if Australia chooses Japan's Soryu,
Like many countries Australia has a number of Senate Committees that seek answers from defence civilian and armed services officers. In late February 2015 in a Senate Committee meeting Senator Nick Xenophon (from South Australia) asked questions concerning Australia's known preference in “competitive evaluation process” for a submarine that is highly compatible with, or already uses US weapons. The relevant US weapons include the Harpoon (short-medium range) cruise missile, Mark 48 heavyweight torpedo, and, in future, the Tomahawk (longer range) cruise missile.
“Do any German designed submarines carry US weapons?”
To this they responded that:
“Defence is not aware of any German designed submarines that carry US weapons”.
Senator Xenophon then pointed out that a range of Wikipedia articles and official US government documents confirmed that a number of German designed submarines used or can use some US weapons, including those owned by South Korea (in Australia’s region) Greece, Turkey, Israel and Brazil.
Most have accepted the response to Senator Xenophon as ignorance or oversight, but there is an equally likely explanation.
Naturally Abbott does not want Xenophon or the Labor opposition to be able to say "but the Navy and DMO have already indicated that "compatibility with US weapons" is a non-argument when claiming Japan's Soryu is preferable to the German contender".
The defence heads therefore had to rely on seeming ignorance. To provide political ammunition to Senator Xenophon would be entering into the highly political submarine selection issue, after all...
Another possibility is that the Prime Minister's Office took carriage of the question, provided the wrong answer and the defence heads were forced to live with it. It has already been established that the Prime Minister's Office has taken much of the political carriage of the Soryu issue. After this office handled the Senate Committees questions the defence heads had to wear the acute embarrassment at the Senate committee meeting on the day.
So all this mean's that Abbott's Captain's pick of Japan's Soryu, for the sake of alliance with Japan and the US's advocacy of the Soryu, is influencing otherwise expert testimony on Australia's multi billion (taxpayer) dollar submarine selection.