The King's Own Scottish Borderers have taken another step towards their disappearance later this year.
Despite a long campaign the KOSB merger is going ahead
They are now a battalion of the new Royal Regiment of Scotland and will soon amalgamate with the Royal Scots to form the Royal Scottish Borderers.
The regiment's traditional Glengarry cap is being replaced by the new Tam O Shanter bonnet.
KOSB commanding officer Lt Col Rob Jefferies said it was a sad day but time to embrace the future.
He told troops at a special ceremony in Northern Ireland: "For all of us, without doubt, there will be great sadness as we wear our cap badge for the final time.
"I have no doubt that the Royal Regiment of Scotland will be the finest regiment in the British Army.
"We must prepare to wear our new cap badge with the same pride that we have worn our own," he said.
However, a former commanding officer of the KOSB, Clive Fairweather, said the day was a "tragedy" for the regiment.
He said: "I can't help thinking that what we are doing is diluting and, if you like, a watering down of standards.
"As a former CO of the KOSB I really do feel we are seeing here a tragedy - and an unnecessary one at that."