Sanders, who became chief of the general staff this month, used his first speech to warn that the army must be ready to fight to "avert conflict", in what appeared to be an appeal for modernisation and possibly further defence spending.
"While Russia's conventional capability will be much reduced for a time at least, (Russian President Vladimir) Putin's declared intent recently to restore the lands of historic Russia makes any respite temporary and the threat will become even more acute," Sanders said in a speech at the Royal United Services Institute, a defence and security think tank.
"We don't know how the war in Ukraine will end. But in most scenarios Russia will be an even greater threat to European security after Ukraine than it was before."
He said the army should focus on boosting readiness so troops could be deployed quickly, and on urban combat and rebuilding stockpiles. He described the choice facing Britain as its "1937 moment" in what appeared to be a reference to when Nazi leader Adolf Hitler invaded Austria.
"We're not at war, but we must act rapidly so that we aren't drawn into one through a failure to contain territorial expansion," he said.
"From now the army will have a singular focus to mobilise to meet today's threat and thereby prevent war in Europe."
(Reporting by Kylie MacLellan and Andrew MacAskill, writing by Muvija M and Elizabeth Piper, editing by William James)
