Andrew McIntosh, 38, amassed an arsenal of guns, ammunition and CS gas and sent letter bombs to government offices and industrial targets in a two-year campaign for the Scottish National Liberation Army, the Crown alleges.
Between January 1992 and August 1993, when he was arrested, he is also accused of planting mortar devices and making hoax bomb threats that brought central Aberdeen and Glasgow to a standstill.
Mr McIntosh, a courier from Aberdeen, denies 18 charges of unlawfully acquiring and retaining firearms, ammunition, explosive substances and detonators intending to endanger life and cause serious injury.
Gordon Cantlay, 33, who met Mr McIntosh at an Aberdeen gun club, told the High Court that last July Mr McIntosh said he had sent a letter bomb to the Scottish Office 'through a contact in Dundee'. He said Mr McIntosh had 'extreme nationalist views' and 'connections' with the SNLA.
The trial, which was adjourned until today, is expected to last up to four weeks.