The Chief of the Defence Staff has warned the threat from terrorism has increased.
Speaking during an annual event at the Royal United Services Institute in London (RUSI), General Sir Nick Carter stated the present is a period of "phenomenal change" and the so-called Islamic State group (IS) still pose a threat to the world.
The military chief citing last week's attack at London Bridge as an example.
"Daesh, and the extremist ideas it represents, has absolutely not been defeated – indeed the threat from terrorism has proliferated, as was sadly demonstrated once again in last Friday’s attack at London Bridge," said General Carter.
General Carter said the next Strategic Defence and Security Review needs to answer some significant questions - referencing adaptations required of the military and the entire Government.
The 2019 Global Terrorism Index has named the UK the EU country most affected by terrorism, and also among the top 30 countries affected worldwide.
The London Bridge attack took place on 29 November, weeks after the UK's terrorism threat level was downgraded to "substantial" from "severe" - meaning attacks were thought to be "likely" rather than "highly likely".
Touching on worldwide defence concerns, General Carter warned Russian activity in the North Atlantic and in NATO operational space "is at a post-Cold War high".
Also mentioned was Turkey's cross-border offensive in northern Syria, against the Syrian Democratic Forces led by Kurdish militia.
The Kurds had helped the United States in the fight against IS before Donald Trump controversially withdrew troops from the region.
General Carter described Syria as "a tinder box that could easily ignite a wider conflagration", with more than 1,000 armed groups fighting there - all with "very different agendas."
Hostility in the Persian Gulf, Yemen and Libya were also mentioned, with General Carter adding that conditions in parts of the world are "not conducive to reducing the growth of extremism".
While the call for a development in strategy was clear, achievements in defence and security so far were also acknowledged.
Operation Relentless, the longest operation ever carried out by the British military, was praised on its 50th anniversary year - nuclear deterrent submarine patrols performed around the clock since 1969.
General Carter added: "We are in a period of phenomenal change – more widespread, rapid and profound than humanity has experienced outside of world war... more sustained than the two world wars of the last century combined.
"Modernising will only get us so far – what is needed is a step-change in how we fight, in how we run the business, in how we develop our talent, in how we acquire our equipment, and in how we provide support – this requires transformation.
"As we enter the fourth Industrial Revolution, it is the same challenge and opportunity that faced our predecessors as they went from sail to steam."
Cover image: General Sir Nick Carter speaking at RUSI (Picture: MOD).