Welcome back to Yours.Sincerely, our Friday dive into the letters and comments on what you decided was the topic of the week.

Readers took to their keyboards after the government’s decision to purchase nuclear-powered submarines as part of the AUKUS pact, the country’s biggest military spend since WWII.

• In the end, courage prevailed over timidity, wrote journalist Matthew Knott. The Albanese government revealed the estimated cost of a fleet of eight nuclear-powered submarines was more than $350 billion. Readers crunched the numbers:

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P1 The best defence does not come cheap. Hope and work hard for peace but prepare for the worst.

Mais $400 billion is big money, but that’s nothing compared to a partial destruction of Sydney, Brisbane, Perth or Melbourne by the enemy’s hypersonic missiles launched from their nuclear-powered submarines a few hundred nautical miles from our door steps.

AppleCrumble The irony is, of course, that we can thank China for having to do this; and being able to afford to do this.

Jake I am not sure why so many of the commenters are outraged at the expenditure on defence capabilities. The happy, trippy, hippy peace, love and mung beans era ended in about 2015. Australia is facing an existential threat. Globalisation is over – the US is pulling back from being the world’s policemen of trade routes. China is trying to control shipping routes we need to get stuff and sell stuff. If we don’t act, our country could be crippled by a virtual blockade in coming years. We are the world’s biggest island after all – about time we projected some meaningful naval power. Appeasement never worked. If you want to deter bigger predators from attacking you, you need to be prickly like a porcupine. Nuclear subs may be expensive but they are formidable.

John Court, Denistone Naval hardware is expensive, may only rarely be used in anger, but seems apt for a land “girt by sea” at a cost of just less than 1 per cent of GDP over 30 years.

Wylah What a joke. If we believe China is the big bogeyman, why would China wait 10 to 30 years before attacking. Or do we think they will keep trading with us for the next 10 to 30 years and then attack. Totally irrational. Weep Australia, you have been dudded.

Frances Taylor, Mosman Why do I feel that Australia is a pawn in this triangle? The contest in this part of the world will be well and truly over before our first submarine has been delivered.

George Fishman, Vaucluse When thinking AUKUS subs deal, think “known knowns, known unknowns and unknown unknowns”.

• International security and strategy specialist David Livingstone wrote that the prudent planning of defence preparation requires genuine intellectual rigour. Instead, he said, all that was evident in the submarine announcement was intellectual rigor mortis. Letters writers and online comments told us what they thought:

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Alan Morris, Eastlakes The analysis by David Livingstone is very persuasive. If correct, it suggests that the government has made a monumental error and wasted a huge amount of money. What a total debacle.

AD These new subs seem like a terrible tactical decision and we can only conclude that the decision cannot be based on military needs or tactics.

Troy My view is that we are purchasing the submarines to ensure that the US will come to our assistance if required. It is effectively a payment for future protection.

Tony Simons Anything that Morrison touched is suspect. Dutton supporting Labor for the first time in nearly one year only reinforces how much jingoism is at play. AUKUS is the worst policy decision in more than 100 years.

Michael Cosgriff I wonder how long it will be until the stories are written about just who has profited from this decision to commit to this huge expenditure.

Brian Haisman, Winmalee At last. Someone talking sense. AUKUS has always felt like the last gasp of a bunch of nostalgic generals. Add to that a moribund, fading Britain and a disastrously polarising and ineffective US. What a pig in a poke we’ve bought. Just plain dumb. The only bright spot is that after our efforts with the French, Australia has some useful experience in getting out of a crook deal.

Silvia Salisbury, Belmore As an extremely expensive contract should there not have been a “cooling off” period to allow for more discussion and avoid another Macron embarrassment and to really defend the lives of the most vulnerable Australians?

nevermind Our close neighbours up north, such as Indonesia and Malaysia, are much more worried and irritated by Australia possessing nuclear subs than China is. To suggest that our nuclear subs can deter China from taking Taiwan by force is purely laughable. If we really want to defend our own territory and coasts, drones are far more effective and economically viable than the dumb sub deal and may also provide our local technology sector a boost as well.

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Kasekuchen I can’t believe our politicians and military experts are really that stupid. This whole sub saga must all be theatre for some political purpose. Everybody seems to expect war with China around the turn of the decade, that’s even before we get the US subs. And after that war, we won’t be building anything at all.

artusj The sheer financial scale of this commitment is disturbing. Ignoring inflation and costs over runs, it is an expense that will saddle us for generations. Back of an envelope calculation is $16,000 for every man, woman and child. Just for eight subs.

Frankly What I find missing in the discussion about the worth of this $368 billion investment in nuclear submarines is the cost and effectiveness of alternative systems, such as land-based, mobile intercontinental ballistic missiles. I suspect we would get more bang for our buck and if the only consideration is to have a serious deterrent, then there should have been more public discussion of the alternatives.

• Former prime minister Paul Keating launched an extraordinary attack on the Albanese government over its adoption of the AUKUS pact, accusing it of making the worst foreign policy decision by a Labor government since the attempted introduction of conscription in WWI. Here’s what you wrote:

Dorothy Kamaker, Whale Beach If only Paul Keating could concentrate on the issues and deny himself the vitriolic assassinations, he’d be listened to, not just heard. He’s too easy to dismiss and that’s at a cost to all of us.

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rc Don’t think Keating needs to worry too much about ceding our sovereignty to the US – it’ll probably implode with its own civil war in the not too distant future.

cipher Thank you, Paul Keating, Australia’s solitary elder statesman. At least you have the guts and commitment to say what needs to be said. It’s our nation’s future well-being you are talking about.

Paul Duncan, Leura Keating is right, the AUKUS submarine deal is the biggest mistake since Federation. A million dollar drone armed with a million dollar torpedo can find and sink a submarine and that is just with today’s technology. The list of sound and acceptable arguments against this absurd plan is endless.

Patsy Asch, Armidale One does not have to agree with Keating about the threat of China, to thank him for raising the significant point that there was no public, community discussion of our security options before the AUKUS agreement was signed. We are committing a future government to spending billions of dollars, most to foreign countries. Let’s have a serious discussion of what this will mean, both in terms of defence but also other impacts, not just a blast about which politician challenges which.

Brian McDonald, Kensington Thank heavens for Paul Keating’s strident denunciation of the ill-considered AUKUS deal. Twenty-four hours’ consideration by Albanese before approving a deal with such momentous strategic and financial ramifications is utterly ridiculous. Keating is to be applauded for standing up for principle even if it means being denigrated by his own party.

dpoms Keating, yesterday’s man.

nulla sapientia Paul Keating. Australia thanks you.

• You can join the conversation at smh.com.au in the comments sections of each article, and in letters to the editor in print and online. See you next Friday. Yours. Sincerely, Pat Stringa, letters editor