By Steven McKenzie
Highlands and Islands reporter, BBC Scotland news website
The trenches could have been dug by Army soldiers or Royal Marines
A second set of trenches dug for training purposes during World War I has been investigated by experts in an area that saw intensive use in wartime.
The line of three trenches lies about two miles from where other remains were found to have survived in a field in Ross-shire last year.
The Royal Commission on Ancient and Historic Monuments of Scotland (RCAHMS) have investigated the site.
The farmer has never ploughed the field preserving the system for decades.
RCAHMS were made aware of the latest trenches during a trawl through archive images of the area around Invergordon, a key port for the Royal Navy before, during and after WWI.
The commission has been collecting, recording and interpreting information on the architectural, industrial, archaeological and maritime heritage of Scotland for more than a hundred years.
Allan Kilpatrick, of RCAHMS, has visited both trench sites.
He said: "They may have been dug by territorial units, regular soldiers or marines based in the area.
"They have been preserved because the farmer never ploughed the field as the ground is of a poor quality for farming.
"The trenches have been dug into a gravel terrace, meaning it was easy for the men to dig but also for subsidence to happen. The trenches have been almost completely filled in because of subsidence."
Training trenches have also previously been recorded in the Pentland Hills, near Edinburgh.
Mr Kilpatrick said Invergordon and the surrounding area had seen "intensive use" in both world wars.
The first set of trenches was identified by RCAHMS last year
Look-out posts and gun batteries were built on the coast at nearby Cromarty for use during WWI and added to during World War II.
At Inchindown, near Invergordon, oil storage tanks were dug into a hillside to conceal and protect them from enemy attack during WWII.
Trench warfare dominated WWI.
After the Battle of the Marne in September 1914, the German army was forced to retreat after failing to bring about the surrender of France.
Rather than give up territory which they already held, the Germans dug in to protect themselves.
The Allies could not break through so followed their example.
Trench lines soon spread from the North Sea to Switzerland.
Britain's last surviving WWI veteran Harry Patch died aged 111 in July this year.