The submarine, flying the French flag, was towed by tugs into the Faslane naval base on Gareloch on August 2. It was spotted and photographed from the shore by anti-nuclear campaigners at the Faslane Peace Camp.
The campaigners identified the boat as one of the four French Triomphant-class that usually carry nuclear weapons. They say this is the first time a nuclear-armed French submarine has been seen visiting the Clyde.
The first of the class, Le Triomphant, collided with the British submarine, HMS Vanguard, which carries Trident nuclear missiles, three years ago. The accident happened somewhere in the Atlantic, but details have been kept secret for national security reasons.
The SNP defence spokesman, Angus Robertson MP, said the French visit prompted serious questions. "Weapons of mass destruction are not welcome on our shores," he said.
"The Scottish Government, the Scottish Parliament and the Scottish people are overwhelmingly opposed to nuclear weapons and their continued presence in Scotland. The visit also raises serious safety concerns."
John Ainslie, co-ordinator of the Scottish Campaign for Nuclear Disarmament, said: "It is insensitive for the Force de Frappe, the French nuclear force, to make its first appearance at Faslane just as Scotland is preparing for a referendum on independence."
A Ministry of Defence spokesman said: "It is our policy not to discuss submarine operations as this may compromise the security of these vessels.
"HM Naval Base Clyde is the home of the UK submarine service and as such hosts a wide variety of vessels from Nato countries and our allies throughout the year."