Fears have been raised the RAF may need to provide supplies to Orkney communities amid warnings their ageing ferry fleet could collapse.
Councillors have been planning for the eventuality that one, or more, of the council-owned vessels could be out of action for months.
The outer isles could be cut off for weeks on end if the vessels break down at the same time.
Replacing the nine boats – aged between 27 and 50 – would cost an estimated £400 million.
RAF drops and airlifts have been discussed at council meetings as members considered a scenario where all of the vessels were out of action.
Councillor Kristopher Leask said there is growing “pessimism” about the time it was taking to get a deal with the Scottish Government to buy new boats.
Speaking with the Herald on Sunday he said the council will need to start exploring what an evacuation may look like without the ferry replacements.
“This is not something we are expecting on the horizon by any means,” he stressed.
“However, it’s part of our responsibility to crisis plan. We’re now in meetings starting to talk about what would happen in the worst-case scenario.
“We’re increasingly aware that the fleet is of such an age. So if it were to be the case, for example, that two of our North Isles ferries went out of action for six months, nine months, what would that look like for our islanders, how would they get the services they have a complete right to?”
This comes after Orkney councillors voted earlier this month to explore self-governance.
‘Put simply, we cannot run an unsafe vessel’
An Orkney Islands Council spokeswoman confirmed the local authority has started emergency planning for several ships being out of service.
The NHS, and other essential services, have also started making plans.
She said: “Given the age of the fleet and the absence of a funding commitment from the government, council officers have been asked to make preparations for the mitigation and service changes that will be required if there was no access to the current ferry provision at some point in the coming months or years.
“Our partners in NHS and other essential services operating in the community have been asked to make similar preparations. Put simply, we cannot run an unsafe vessel – and that might mean that eventually, we won’t be able to run a boat at all.
“We’re also exploring ways to provide essential passenger-only transport links to these communities when the current fleet is unavailable.
“As part of these plans UK and Scottish Government agencies – and the wider public and private sector – will be asked to provide assurances for communities around their plans to ensure the provision of essential freight, energy, and fuel stocks, as well as other aspects of services and support that are not devolved to local councils when the current fleet is no longer safe to operate.”
A Transport Scotland spokesman said the Scottish Government remains “committed” to the Orkeny Internal Ferry Replacement Task Force.
He said: “The Scottish Government remains committed to the Orkney Internal Ferry Replacement Task Force.
“The next meeting will be in August with Fiona Hyslop, Minister for Transport, and will take place in Orkney.”
