Ministry of Defence Police are now involved in the investigation into the discovery of live bullets in Angus.
A cache of up to 50 rounds of ammunition in a bandolier was recovered from Keptie Pond in Arbroath during a clean-up operation at the start of October.
The rounds appeared to be 5.56mm NATO standard type used in the SA80, the standard issue service rifle used by the British armed forces since 1987.
They were discovered just two miles from RM Condor which is home to 45 Commando Royal Marines and 3 Commando Brigade.
It also houses 7 (Sphinx) Battery, part of 29 Commando Regiment Royal Artillery, 2 Signals Squadron from 32 Signals Regiment and 30 Commando Information Exploitation Group Royal Military Police Detachment.
The Ministry of Defence-owned rifle range and training area at Barry Buddon is 11 miles away, adjacent to Carnoustie Golf Links.
A Royal Navy spokesman said: “We can confirm that the Ministry of Defence Police are currently working with Police Scotland to investigate this incident.
“It would be inappropriate to comment further until the investigation is complete.”
A source close to the investigation said it was “inevitable” the Ministry of Defence Police would be called in.
“These bullets are military issue,” he said.
“They will be tracing the batch number on the bottom of the rounds.
“This will enable them to determine whether they are from Condor or the Barry Buddon ranges.
“There is no way a civilian has been running around with all those rounds in a bandolier.”
MOD police officers protect sites of national importance and carry out sensitive work which includes lending their specialist skills to other police forces.
It is not known whether the rounds found at Keptie Pond are ‘standard’ or ‘enhanced performance’ versions of the ammunition.
The unusual find was made during a monthly clean-up by local group Keptie Friends.
Testing of an underwater metal detector has already taken place as volunteers prepare to sweep the pond to discover if anything else is lurking beneath the surface.
Keptie Friends chair Morag Lindsay said: “We’ve decided to invest in another couple of pairs of waders so that any volunteers who come along are kitted out to go into the pond.
“Once these arrive we’ll check the weather for a better day and we’ll go out to sweep the area.”
A Police Scotland spokeswoman said: “Enquiries are continuing.”