Speaking at the Royal United Services Institute Sea Power Conference in London, Mr Williamson said it could be difficult to explain why the UK needs to project military power around the globe when it has the ultimate insurance of the Trident nuclear deterrent.
In comments likely to be seen as aimed at Chancellor Philip Hammond, he said investing in the military was about “making sure things do not happen”.
“You do not want to be in a position where your only deterrence against threat and against aggressors is a nuclear deterrence. We have got to talk about deterrence being full-spectrum, right across the board,” he said.
“It is sometimes difficult to explain to people that actually investing in our armed forces is all about making sure that things do not happen.
“It is about aircraft carriers, it is about a presence in the Pacific, it is a presence in the North Atlantic, it is a presence in the Mediterranean and in the Gulf with conventional frigates and destroyers that are able to say that Britain is interested, Britain cares, Britain will protect our interests and our values.
“If we do not have that conventional deterrence and the ability to deter through conventional forces, then what we will find ourselves in is a place that none of us wish to be in and having to turn to the greatest deterrence of them all.”
Mr Williamson pointed to figures obtained earlier this week by the Press Association through the Freedom of Information Act, showing that in 2017 the Royal Navy had to respond on 33 occasions to Russian vessels approaching UK waters as an example of the continuing threat.
“It goes to show the increasing aggression, the increasing assertiveness of Russia and how we have to give the right support to our Royal Navy in order to give them the tools to do the job and keep Britain safe,” he said.
The Defence Secretary said that at a time of rapid technological change, the Government needed to work with industry to ensure the forces had access to the latest developments far more quickly than at present.
“It takes 15 to 20 years-plus to procure an aircraft carrier. How many models of iPhone will have been procured and developed in that time?” he said.
“If we do not have technology and be able to use technology and bring technology into our ships, into our submarines at a much faster pace, then we will always be behind our enemies.”