A Royal Marine reservist is facing years in jail after stealing a cache of firearms, grenades, plastic explosive and thousands of rounds of ammunition from a military base.
Martin Shannon, 43, was arrested by armed officers outside a supermarket in Winnall, near Winchester, on September 1 after an undercover operation headed by the National Crime Agency (NCA).
The married defendant, who was said to be suffering from post-traumatic stress disorder, admitted 15 offences at the Old Bailey on Friday, including selling some of the guns during the covert sting.
Shannon, of Hayley Close, Hythe, near Southampton, had taken a Diemaco (C8) automatic assault rifle and a semi-automatic Sig sauer P226 handgun from RM Poole in Dorset.
He also pocketed thousands of rounds of ammunition, seven high-explosive hand grenades, plastic explosive, which were all recovered following his arrest.
The ammunition included 5.56mm rounds for the assault rifle - high calibre, high penetration bullets - and 9mm rounds for Sig-sauer handguns.
They are commonly used by armed forces and law enforcement around the world.
Shannon pleaded guilty to transferring an assault rifle, pistol and sawn-off shotgun and cartridges.
He also admitted possession of more ammunition, seven hand grenades, plastic explosive and a shotgun.
The defendant appeared at the Old Bailey via video link from Bullingdon jail in Oxfordshire before Judge Richard Marks QC.
He sported bushy sideburns and wore a black and white shirt for the short hearing.
Shannon spoke only to enter his guilty pleas and the case was adjourned for a psychiatric report on post-traumatic stress disorder (PTSD).
Defence barrister Kevin Hill said Shannon had a psychiatric history which may offer some mitigation in the case.
He told the court: "The concern is post-traumatic stress disorder that may well have some bearing on sentence in this case in terms of mitigation available.
"It is a case where there might be significant mitigation that would assist the court in the form of psychiatric assessment."
Judge Marks agreed and remanded the defendant in custody until sentencing on December 16.
He said it was a case of "considerable seriousness" and a "significant sentence is inevitable".
He told Shannon: "It is intended a psychiatric report be obtained to understand something about your background, in particular it is said that you may be suffering from PTSD that may impact on these offences.
"In the meantime, you will need to remain in custody and I am sure you will understand the fact I am adjourning for a report is not an indication that the case will be dealt with in any other way than immediate imprisonment.
"The only issue will be as to the length of the sentence."
Shannon was arrested by officers from the NCA's Armed Operations Unit, working with the Joint Operations Unit from Thames Valley Police and Hampshire Constabulary.
A Ministry of Defence spokesman said: "We take the security of weaponry very seriously and have robust procedures to deter and prevent losses and thefts which are constantly reviewed.
"In this case it would be inappropriate to comment whilst legal proceedings are ongoing."
At the time of his arrest, Rob Lewin, head of specialist operations at the NCA, confirmed there was no link to terrorism.
Shannon pleaded guilty to two counts of having an explosive substance; three counts of transferring a prohibited weapon; one of transferring prohibited ammunition; eight counts of possession of ammunition and one charge of possessing a shotgun without a firearms certificate.