Workers at the Atomic Weapons Establishment are to stage two 48-hour strikes in a long-running dispute over pensions.
Unite said 600 of its members at AWE's two sites at Aldermaston and Burghfield in Berkshire will walk out for 48 hours from January 18 and 30.
The union said workers felt "deeply betrayed" as promises made a quarter of a century ago guaranteeing their pensions, when they were transferred from the Ministry of Defence to the private sector, have been broken.
The union is protesting at plans to close the defined benefit scheme at the end of the month and replace it with a defined contribution one.
Unite regional officer Bob Middleton said: "It was in the House of Commons in the early 1990s that the then-Tory government made copper bottomed promises to AWE workers regarding the future of their pensions, once they transferred to the private sector.
"It is quite clear that this pledge has been shattered and our members feel deeply betrayed. The hallmark of this dispute is a litany of broken promises.
"The most just course of action would be for the pension scheme to be taken back by the MoD.
"The four days of strike action later this month are not being taken lightly. It is not a 'political' strike, but one taken reluctantly by our members who have no desire to see thousands of pounds wiped off their retirement incomes."