Laura Drew is one of those whose charges still stand.
She said many of them were arrested in different places, and a dispute over what counted as public land was why some of them were still facing charges.
"But we're hopeful the rest of the case will fall apart today," she said.
"We've been through this lengthy process, more than a year since the arrests.
"It's an impingement on our rights to freedom of protest."
Emma Cullen is one of those whose charges were dropped, and said the move showed police action had "interfered with our right to freedom of speech".
"We were arrested on public land while exercising our lawful right to protest.
"I'm glad to have been let off these charges today, but I'm going to keep coming to court to support everyone else who stood up against the arms trade.
"We all know who the real criminals are.
"It's not the peace activists, it's the arms dealers profiting from death and destruction."
Despite the court case Peace Wellington is continuing its campaign against the arms trade, with a petition being handed in to Parliament at 6pm today.