The Head of the Army has suggested that withdrawal from Germany could be halted so that troops can maintain quick access to Eastern Europe in the event of Russian hostilities.
General Sir Nick Carter said that the threat from Russia meant that military chiefs were considering retaining bases that troops are set to withdraw from by 2020.
Under the 2010 Strategic Defence and Security Review, all British troops in Germany were earmarked for recall back to the UK, with the final units set to leave the county in 2019 and the bases there closed.
But Gen Carter said when it comes to threats, it is important to recognise that "readiness is about speed of recognition, speed of decision-making and speed of assembly".
He said the Army is testing the ability to deploy over land by using road and rail, but that it is "also important to stress the need for a forward mounting base".
He also warned that Britain's ability to respond to threats will be reduced if the UK does not keep up with its enemies.
He pointed to Syria, where General Carter said the Kremlin has repeatedly and publicly demonstrated its long-range strike capability.
He said that Britain must also look closely at how countries are now being more creative in the ways in which they exploit the seams between peace and war.
"Our ability to pre-empt or respond to threats will be eroded if we don't keep up with our adversaries."
He said: "State-based competition is now being employed in more novel and increasingly integrated ways and we must be ready to deal with them.
"The threats we face are not thousands of miles away but are now on Europe's doorstep - we have seen how cyber warfare can be both waged on the battlefield and to disrupt normal people's lives - we in - the UK are not immune from that."
Mirroring Kremlin concerns made by others, General Carter highlighted how last year Russia undertook simulated attacks across Northern Europe - from Kaliningrad to Lithuania.
Last month the chief of the defence staff Air Chief Marshal Sir Stuart Peach also addressed the threat of Russia and said the UK's military has prioritised the protection of undersea cables from the Kremlin because if they are cut or disrupted there would be an immediate and "potentially catastrophic" hit to the economy.
And using her address at the Lord Mayor's Banquet in London, Prime Minister Theresa May also said last year that Russia had "mounted a sustained campaign of cyber espionage and disruption" against other countries.
During his speech, General Carter stressed that Britain "must take notice of what is going on around us" or that the ability by the UK to take action will be "massively constrained".
"Speed of decision making, speed of deployment and modern capability are essential if we wish to provide realistic deterrence," he added.
"The time to address these threats is now - we cannot afford to sit back."
General Carter's comments come during a period of widespread speculation about possible cuts to the defence budget.
There have been calls to increase defence spending to 3% of GDP from some MPs.
It comes amid reports there are plans to cut the armed forces' strength by more than 14,000, as well as the combination of elite units of paratroopers and Royal Marines to save cash.
But, in the Commons during Defence Questions last week, Gavin Williamson claimed "hard work" is taking place across Government to give the "right resources" to the armed forces.