Hundreds of workers at the Faslane nuclear base have staged a walk-out, the first in 42 years at the plant, after rejecting what they say is a derisory pay offer from employers.
Union leaders said talks had failed to secure a fair deal for members while contractor Babcock paid "eye-watering" bonuses to top directors.
Unite said about 800 workers joined today's two-hour walk-out at the Faslane and Coulport naval bases on the Clyde this morning.
Further one-hour stoppages are planned from tomorrow as well as a work to rule and an overtime ban.
Unite national officer Ian Waddell said: "It's with a real sense of disappointment that our members are taking strike action for the first time in 42 years at the Clyde naval base.
"It's the culmination of months of fruitless discussions with Babcock over a fair pay rise for our members.
"They were initially offered a 1% pay rise in the same year that directors were given a 9% pay rise and shareholders enjoyed a 16% increase in their dividend.
"The company made £234 million in profit; they can easily afford a fair pay rise for our members. They have been very clear - all they are looking for is a 3% pay rise, no strings attached.
"To take that decision to go on strike when you've never done it in your working life is one of the most difficult decisions they will have had to make. But they delivered a very clear majority.
"There was a 95% Yes vote for strike action and they rejected the company's latest offer of a two-year deal with strings attached by 99% at a meeting last week.
"It's with a real sense of grim determination that they started strike action today."