Filed at 7:37 a.m. ET

DENVER (AP) -- Three nuns accused of defacing a missile silo by swinging hammers and painting a cross on it with their own blood were carrying out a peaceful protest that did not jeopardize national security, a defense attorney said.

Sisters Ardeth Platte, 66, Jackie Hudson, 68 and Carol Gilbert, 55, are accused of breaking into a Minuteman III missile silo site on Colorado's northeastern plains Oct. 6. They have been charged with interfering with the nation's defense and causing property damage of more than $1,000.

Hudson's attorney, Walter Gerash, said the sisters entered the N-8 site to protest. They read Bible verses about pounding swords into plowshares and sang hymns.

The nuns said they were compelled to act as war with Iraq moved closer and because the United States has never promised not to use nuclear weapons.

Assistant U.S. Attorney Robert Brown said the sisters refused to leave the missile site when officers ordered them to do so. He said the Minuteman and other nuclear missiles have been vital to the nation's defense and have deterred other nations from using nuclear weapons.

``It would have been nice if they never were invented. But they were,'' Brown said.

Gilbert and Platte both lived at Jonah House, a communal residence for pacifists founded by Philip Berrigan in Baltimore. Hudson belongs to a similar group in Poulsbo, Wash. All joined the Dominican order in Grand Rapids, Mich.

Platte, who is representing herself, tearfully told jurors Tuesday that the peace protest was worthwhile, even if she and the others are jailed. She said she hoped the demonstration would make people think more about the weapons.

The nuns could receive up to 30 years in prison if convicted.

``If we have to spend the rest of our lives in prison we will,'' Platte said, fighting tears. ``We have friends who are in the war zone. We must do more for peace.''