Jimmy Massey was giving evidence in the Dublin Circuit Criminal Court trial of five antiwar protesters accused of criminal damage of a US aeroplane at Shannon Airport in February 2003.

Mr Massey was a platoon sergeant in the US Marines stationed in Kuwait in the lead up to the outbreak of the Iraq war and served there following the invasion until May 15, 2003.

The accused have pleaded not guilty to two counts each of causing damage without lawful excuse to a naval plane, property of the United States Government and to glass door panels, property of Aer Rianta at Shannon Airport on February 3, 2003.

They are Ciaron O’Reilly, an Australian national and Damien Moran, aged 25, both of South Circular Road, Rialto; Nuin Dunlop, aged 34, a US citizen and counsellor living on Walkinstown Road, Dublin; Karen Fallon, aged 35, a Scottish marine biologist living on South Circular Road, Rialto; and Deirdre Clancy, aged 35, a copy editor of Castle Avenue, Clontarf, Dublin.

Mr Massey told Mr Brendan Nix SC, defending Ms Fallon, that prior to invasion he was briefed of the terms of the Geneva Convention and rules of engagement. He said he was told that intelligence reports "painted every Iraqi as a potential terrorist".

In response to Mr Nix’s query as to what was their "firing policy". Mr Massey replied: "To shoot first and ask questions later. We were given carte blanche to kill."

Asked by counsel if this was in breach of the Geneva Convention, Mr Massey replied: "Yes sir".

Mr Nix: "Did it happen?" - "It did, many times. Over a three month period more than 30 innocent people were killed that I know of."

Mr Massey, originally from North Carolina, said he joined the US Marines as a 19 year-old and served for 12 years before his honourable discharge in December 2003. As platoon sergeant he was in charge of machine gunners, missile men and scout snipers.

He told Mr Roderick O’Hanlon SC (with Mr Giollaiosa O Lideadha BL), defending Mr O’Reilly and Mr Moran, that Shannon Airport had, since the first Gulf War, "always been used as a military supply and logistics port".

Mr Jeffrey Oxley, a former Royal Air Force Group Captain, agreed with Mr O Lideadha, that a supply plane could be a "legitimate target" in a war situation.

Mr Oxley said it would be difficult to see an empty supply plane as a primary target but agreed it would be attacked if it was the only target available in order to remove an asset from an opposing force.

Mr Oxley agreed with Mr Michael O’Higgins SC, defending Ms Dunlop and Ms Clancy, that there was significant resistance in western Europe in the build up to war and that the UK and US governments needed to be aware of such.

Mr Oxley agreed with Mr O’Higgin’s suggestion that governments would have been concerned when they heard a plane had been disabled, "married to a clarion call".

Mr O’Higgins suggested that some military operations which have little chance of success are sometimes carried out by a small number of people in order to "inspire others".

Mr Oxley responded that in such a situation one could not foresee events but would need to have a good idea of the outcome.

Ms Fallon, giving evidence in her own defence, told Mr Nix that she damaged the plane "primarily to stop them killing people and destroying their hospitals and waterworks. It’s OK for us, no one is bombing us everyday."

She said she had seen for herself an increase in military traffic at a naval base near her home in Scotland in December 2002 and January 2003.

She said she honestly believed she could "make a difference" and said if her actions "could have saved one life, then it is worth it".

Ms Fallon told Mr Conor Devally SC, prosecuting, that she carried a real hammer aswell as an inflatable football hammer into the hangar and was "kind of frightened". She said she carried the large inflatable as she thought it would have been "hard to shoot someone with a green, white and gold hammer".

She denied a number of suggestions by Mr Devally that her actions were "protests" against the war aimed at highlighting the situation and bringing others to her point of view.

Ms Fallon also denied that she was now repeating a "mantra" about saving lives. She said she went into the hangar thinking she could have been shot but the event was now being turned into "some smutty little thing for the newspapers".

The jury earlier heard that repairs costing over $2.5m (€2m) were carried out on the US navy supply plane which the five accused admit they hit with hammers.

The hearing continues before Judge McDonagh and a jury of five men and seven women.