A campaign has been launched to remind civilians to stay away from military training areas after hundreds of "near misses" in recent months.
The campaign "The Training Area Isn't..." is aimed at civilians who are hiking, biking or having campfires or parties on the land.
The Ministry of Defence (MOD) maintains and preserves 190,000 hectares of training estate in the UK, preparing military personnel for operations and deployments around the world.
The MOD is also responsible for the safety of those using the land, which often attracts civilians due to its scenery.
Across the south-east and the west, training estates are seeing an increasing number of incursions, as rural land is built on and people seek green spaces to explore.
In the past four months, there have been at least 326 incursions at Catterick Garrison in North Yorkshire, with hundreds logged as "near misses" - when unauthorised users come within 200m of a live exercise.
Warrant Officer 1 Martin Robson is part of a small team training to be safety marshals at Catterick.
He said: "My job basically is the military police of the training area – there to look after troops and stop unauthorised civilians.
"A few of them will argue the case, saying it's MOD land, therefore, taxpayers' money.
"We’ve had campers, kids camping, we called for the police assistance with that one.
"The mum and dad wanted a few hours alone, so they took the kids up in a tent, set up the tent, chucked the kids in the tent and they went back home and left the kids."
Regional Commander for Training Estates in the North of England, Lieutenant Colonel Mark Holden, said civilians are welcome but must stay on assigned footpaths and bridleways for their own safety.
"We absolutely want people to enjoy the area and the point to make is: Just because it looks empty, doesn’t mean they’re not there," he said.
"We’re focused on keeping everyone in the area safe whether they’re authorised to be there or not. If they’re not, we encourage them to leave."
The campaign, which is being run through posters and online, seeks to educate the public about the risks.
Catterick, the largest garrison in the UK, is the first to run the campaign and it is likely to be used across the country in the coming months.