A new Royal Navy surveillance ship is to be built to protect "critical" undersea cables.
Defence Secretary Ben Wallace warned "the lights could go out" if national infrastructure was lost, and the cables were "incredibly important".
He also told the BBC's Andrew Marr that Russia had "taken a deep interest" in the cables and the UK would be "deeply exposed" without further measures.
It comes ahead of Monday's publication of the defence command paper.
The document will give more detail for the armed forces on the conclusions of the integrated review of the UK's foreign and defence policies.
But some parts were already announced this week, including the lifting of the cap on the number of nuclear warheads the UK holds in its stockpile.
The government had previously committed to reducing the level to a maximum of 180 by the middle of the 2020s, but the move would allow the number to reach 260.
Mr Wallace said it would ensure the country's nuclear deterrent was "credible", and would still be lower than other nations - pointing to France, which has 300.
But Labour's shadow foreign secretary Lisa Nandy said the proposal had "baffled" opposition parties and they would not support it until the measure had been justified by the government.