The Defence Secretary has said a new £132 million submarine-hunting aircraft facility is "integral" to defending the UK from the increasing threat from Russia.
Gavin Williamson cut the first turf for the new home for the Poseidon marine patrol aircraft at RAF Lossiemouth in Moray.
Due to be completed in 2020, it will house nine Poseidon planes which carry missiles able to destroy submarines.
Their key role is to protect the Trident nuclear deterrent and the two new aircraft carriers and they will also be used to gather intelligence and carry out search and rescue missions.
The new facility will include a tactical operations centre, operational conversion unit, accommodation, training and simulation centre and an aircraft hangar.
Mr Williamson said: "With Poseidon going to be arriving here from 2020, this is going to be absolutely integral in terms of our national security, in terms of dealing with the increasing threat that we're seeing from Russia.
"What we've seen from Russia in terms of the North Atlantic is we've seen a tenfold increase in their submarine activity.
"It is an area of operations which they are absolutely stepping up, using more and more of their submarines.
"As a nation we have to respond to that threat, that's why Poseidon is so important."
The move comes as the Scottish Government sought assurances over the future of the military in Scotland, amid concerns over the future of the Royal Marines in Arbroath.
Scotland's Economy Secretary Keith Brown said: "The Ministry of Defence is now in the midst of a further review which has resulted in speculation about the future of the Royal Marines in Arbroath.
"I urge the Defence Secretary to end those fears once and for all by providing clear assurances about Royal Marine numbers and their long-term future at RM Condor, and to confirm that there will be no further cuts to Scottish bases, personnel numbers, or their ability to carry out essential training."
Mr Williamson, who visited the RM Condor base prior to arriving at Lossiemouth, said:
"It's disappointing when the Scottish Government insist on scaremongering.
"In terms of our commitment to Scotland - we employ 20,000 people in Scotland were going to be employing an extra 470 people here at Lossiemouth as a result of this investment - our commitment is absolute.
"We're absolutely committed to the Royal Marines staying in Condor.
"It's rather disapointing the people try and scaremonger and make people worry about their future."
Following the Lossiemouth visit, the Defence Secretary travelled to Glasgow to view the first completed unit of the new anti-submarine warship HMS Glasgow being built at BAE Systems in Govan.