Two of Orkney's famous Churchill Barriers have been listed by Historic Environment Scotland for the first time.

The barriers were constructed during the Second World War as a defensive measure to prevent enemy ships and submarines from entering Scapa Flow, which housed the bulk of Britain's fleet at the time.

Ordered by then-prime minister Winston Churchill, the rock-and-concrete causeways prevented access from the east into the four channels leading to Scapa Flow.

Today, they provide a vital road link from the Orkney mainland to South Ronaldsay.

Two of the four barriers will be now listed at Category A, meaning they are recognised as being of national or international importance.

The remaining two are not being listed at this time because of development proposals.

Elizabeth McCrone, head of designations at Historic Environment Scotland, said: "Travelling through Orkney now, it's hard to imagine the islands as they were in late 1939, as a bustling naval base, living in constant fear of German U-boats getting past the inadequate block ship and net defences. It must have come as some relief when Winston Churchill gave the order to construct the barriers.

"Nowadays, the original function as defensive barriers is a distant memory, but their importance remains. They serve as a tangible reminder of Orkney's past.

"The listing recognises their fascinating history and will help to keep the features which make them a unique and significant part of the island's history, while still ensuring that they continue to be a vital transport link between the islands."