Ministers have been accused of "hollowing out" the UK's defence capability, after new figures showed 17 maritime patrol aircraft belonging to NATO allies were deployed to a key British airbase last year.
Eight US aircraft, as well as planes from Germany, France, Norway and Canada, were temporarily deployed to RAF Lossiemouth in Scotland between January and November.
The Ministry of Defence said it had "robust" maritime surveillance in place and was committed to spending £3 billion on nine new P-8 Poseidon aircraft to patrol the seas from 2020.
SNP MP Martin Docherty-Hughes said: "These figures reaffirm how disastrous the decision to chop up - quite literally - the RAF's Nimrod fleet in 2010 was."
''While we are always grateful for support from our allies, they must be acutely aware of the hollowing out of UK defence capability that this maritime patrol deficit highlights.
"Coming in the same week that we hear the MoD is delaying the security review yet again, we have to ask if the Tories are taking the decisions to address the real threats we face.
"I would like to hear them restate their commitment to purchasing all nine of the promised Poseidon P-8 aircraft."
Maritime patrol aircraft are designed to undertake long journeys over water, on missions including reconnaissance and search and rescue.
The UK used Nimrod planes for the task for decades, but a project to replace its ageing fleet was scrapped by ministers in 2010 amid delays and rising costs.
In October, American and Canadian maritime patrol aircraft were deployed from Lossiemouth to track a suspected Russian submarine.
That same month then-Defence Secretary Sir Michael Fallon warned of an "extraordinary increase" in Russian submarine activity in the North Atlantic.
The figures obtained by Mr Docherty-Hughes in a written parliamentary question show a marked drop on the previous year.
In 2016, 37 maritime patrol aircraft were temporarily deployed at Lossiemouth, with 21 jets stationed there in 2015.
An MoD spokesman said: "We have robust, multi-layered maritime surveillance including both RAF and international allies' aircraft, as well as sonar-fitted frigates and submarines."
"For the future we are committed to investing £3 billion into nine new P-8 Poseidon aircraft to patrol the seas from 2020."