Any potential enemy would surely know why we are building them, so why not tell the people who will pay for them? (As the first is not due to be completed for at least 15 years, maybe our grandchildren will be still footing the bill.)

Maybe the subs will be needed to protect our essential supplies of petrol that come from Singapore because Australia holds only about three weeks' supply at any one time, so any disruption to that regular delivery would mean Australia would grind to a halt.

There might be a cheaper method instead of those multi-billion dollar subs if we spent part of it on making Australia less reliant on fuel from overseas. Maybe we could build bigger storages for that fuel or, even better, spend some of the money to make Australia less dependent on imported oil.

With support from the government and the cost of just one of those submarines, maybe we could create cheap electric cars, for example, with large solar farms to supply the electricity; that would help reduce the carbon gases that even the military say will be a huge problem if climate change is not challenged.

It does seem strange that we can find billions for an unusual form of 'defence', the submarines, while many of Mr Turnbull's mob are quite reticent about doing anything worthwhile to save our planet for our grandchildren because of climate change.

If the subs are simply for 'defence', it is strange that we are looking so far ahead. Can anyone really predict that sort of a world our children and their children will be facing in at least two decades' time?

Just who are we protecting Australia from in two or four decades' time? Wouldn't it be better to become more isolationist and create a battle line along the north of Australia (maybe with rockets, mines and drones) to make it even more difficult for any potential enemy to land along those crocodile-infested mangrove swamps along our northern coastline?

Maybe the subs' main job would be to monitor the actions of countries around Asia, but the way electronic communication seems to gallop ahead with huge changes every year of so, isn't it a big gamble to spend so much money on something that mightn't even be relative in several decades time?

And all this money spent on defence? How much is being allocated to help make our UN Security Council more democratic, more able to work for world peace and out of the hands of the countries that are the biggest arms manufacturers in the world?

Surely our politicians and their military advisers know why we need to spend so much on this military hardware, but it would be helpful if they gave us a few hints, wouldn't it?