Radar staff helped to monitor the status of a grounded trawler
The remotest island group of the British Isles will be put at risk if a radar station is left unmanned, the National Trust for Scotland has warned.
The Ministry of Defence (MoD) and contractor QinetiQ plan to control the site on Hirta, St Kilda, remotely as part of proposed £50m savings.
NTS, which owns the islands, said staff at the test rocket tracking station helped to protect the environment.
The MoD said it would try to minimise the impact of recalling staff.
NTS said radar personnel were a deterrent against vandalism by visitors and assisted in monitoring potential environmental threats.
A further benefit to NTS is that the military shares travel costs of getting to the archipelago, which lies 41 miles into the Atlantic from the Western Isles.
The radar station is staffed all year, mostly by civilian staff, while trust wardens stay on Hirta from April to September.
Without the assistance of the MoD and QinetiQ the trust said the islands could lose their status as the UK's only dual Unesco World Heritage site.
The radar station on Hirta - the largest island on St Kilda - tracks missiles test fired from ranges in the Western Isles.
On Wednesday the MoD announced a series of proposed changes to how its ranges operate.
NTS, which is in the process of making cost savings of its own, said it would struggle to protect the islands' wildlife and archaeological sites alone.
Chief executive Kate Mavor said: "Without the support of the MoD and the infrastructure that they have in place there, there is no doubt that we would find it very difficult to give St Kilda the level of care and attention that it requires."
She added: "The trust would also face a massive increase in costs to maintain our work there and to deal with the redundant MoD buildings.
"At a time when the organisation is working hard to improve its financial sustainability, this is a cost that we can ill afford.
"However, of more concern is the risk that this proposal poses to the environmental and cultural treasures which make St Kilda so special. I would urge the MoD to give full consideration to these issues, before making any final decision."
Last February radar personnel helped monitor the state of a trawler which ran aground on Hirta during a storm.
The 14 crew were rescued but there were concerns about the risk posed by its fuel and cargo of fish.
Fears rats were on the boat were later allayed after baited traps were laid, but remained empty.
St Kilda has a long association with the military.
During World War I a Royal Navy detachment to Hirta meant regular deliveries of mail and food for sailors and the islands' residents.
However, the end of the war and withdrawal of the unit reinforced a feeling of isolation among the community.
In 1930 the remaining 36 islanders requested to be taken off St Kilda and moved to the mainland.
Defence technology company QinetiQ lists its role in helping to manage the island group in the key facts section of its website.
The MoD said it would work closely with NTS and Scottish Natural Heritage on its plans for the St Kilda station.