Electing a leader, for many voters, is about who should be in charge during those moments of national threat.
It is why the defence sections of the party election manifestos are gone through with a fine-tooth comb.
Defence spending does not only benefit those serving in the Armed Forces, as thousands of jobs are associated with the building and maintaining of warships, submarines and armed vehicles.
Here is a look at what are the main parties are promising on defence, where they differ, and where there are some commitments missing.
– Is there common ground between the parties?
Both the Conservatives and Labour have committed to renewing Trident – at a cost of no less than £31 billion – and to honouring the Nato pledge of allocating 2% of GDP to defence spending.
Tory leader Boris Johnson has gone further than Labour on the money side of things, pledging to increase the Ministry of Defence (MoD) budget by “at least” 0.5% above inflation each year.
The Liberal Democrats have given Trident its backing but would pay for three Dreadnought submarines – due to replace the current nuclear missile-carrying Vanguard submarines in the next decade – rather than four.
The SNP are against Trident and want to scrap it altogether. Leader Nicola Sturgeon told Sky News the “tens of billions” invested in the programme would be better spent on a “conventional defence”, alongside other public services.
– Hang on, isn’t Jeremy Corbyn anti-Trident?
The Labour leader certainly has been vocal in voicing his opposition to nuclear weapons in the past.
As a backbencher he called them “illegal, immoral weapons of mass destruction” and, even on becoming leader in 2015, Mr Corbyn said “no” when quizzed about whether he would use them if he became prime minister.
But those hoping Mr Corbyn would drive an anti-Trident agenda at the top of the party look to be disappointed, following both the manifesto commitment and comments made by a shadow cabinet member.
Shadow defence secretary Nia Griffith used an election debate on defence on Thursday to paint a different picture of her party leader.
She said: “The point is that when you are faced with the ultimate defence and security of your country then you may very well do things that perhaps you would not do in normal circumstances and therefore it will remain as a deterrent.”
– What about defence-related jobs – are they safe?
There is a target in both the Tory and Labour manifestos to keep the building of British military ships and vehicles within the UK.
Labour says it would “keep all Royal Navy and Royal Fleet Auxiliary shipbuilding contracts in the UK to secure a long-term future of the industry and its workers”.
The Tories talk of an “ambitious global” defence programme, which includes building the new Type 31 frigates in British shipyards and a “new generation of armoured vehicles, made in Britain”.
All those utterances, along with the guarantee over Trident, appear to be aimed at allaying job fears at dockyards from Plymouth’s Devonport to the Clyde in Scotland.
– What’s in it for those serving in the Armed Forces?
The Tories are getting behind those serving with the promise of “wrap-around” childcare – where children are looked after both before and after school – and measures to support them once they leave the forces, with an Office for Veterans’ Affairs to be created.
Other sweetener policies include a railcard for veterans, a guaranteed interview if former servicemen or women apply for a public sector job and reductions in National Insurance contributions for employers who take on those who have finished their service.
Labour want to scrap the public sector pay cap, meaning a pay rise for those defending Britain.
The manifesto says veterans will be given access to “lifelong learning and training”, as well as help with health needs, including mental health care, and support to find housing after returning to civilian life.
The party wants to create a representative body, similar to that of the Police Federation.
Jo Swinson’s Liberal Democrats would similarly support improving veterans’ mental health, while also looking to “improve the quality of housing” for service personnel by bringing MoD requirements into line with that of the private rented sector.
The SNP said it also wanted the retention of “existing Scottish bases and regiments”, along with contracts for Royal Navy Fleet Solid Support Ships to be restricted to UK shipyards.
– What isn’t in the manifestos that was promised?
The Prime Minister made a big play of blocking what he called “vexatious” legal claims against Armed Forces personnel if he is put back into Downing Street.
That promise made the manifesto but gone was the firm commitment to the controversial idea of overhauling the Human Rights Act to stop it applying to issues arising before the law came into force in 2000, including those relating to the Northern Ireland Troubles.
Defence Secretary Ben Wallace told an audience at a Whitehall debate on Thursday that it remained a “firm pledge” to change the Act to protect Northern Ireland veterans, despite lack of a mention in the manifesto.
Breaking manifesto pledges remains a political taboo. The Tories’ failure to find space for the Human Rights Act reform in its 59-page policy document will raise eyebrows among those wanting a serious commitment to veteran protection.