Different country-specific links but each says it covers worldwide records and has new data (including for WW2) since last year:-
Ancestry UK until 11:59pm GMT on 12th November
Ancestry CA until 11:59pm ET on 12th November
Ancestry AU until 11:59pm AEDT on 12th November
You need a separate account for each country-specific site (free with no card details taken on registration). You do
not need to click on the Start Free Trial box at top right.
Fold3 until 11:59pm MT on 16th November, which I make to be 6:59am GMT on Monday 17th.
You can sign in with an Ancestry account or create a free Fold3 one. If it detects you're in the UK, redirects you to Forces War Records, which I'm told has the same data. However, at the time of writing they didn't seem to have got this set up and FWR wasn't free.
As always with free periods, save anything of interest on your own device, as you'll need a sub to see it online after the offer closes.
Many of these records are available on other sites, sometimes always free, so check before using up too much midnight oil.
