Almost 2,000 jobs could be axed. The figure was thought to be about 1,000 when the plan was revealed on Monday.
As many as 7,000 more jobs in BAE’s supply chain could also be affected.
The union has criticised the government for channelling defence spending to overseas manufacturers.
The heaviest blow will fall on BAE’s factory at Warton in Lancashire, where 1,000 job losses are expected. The site assembles Eurofighter Typhoon jets.
Also hit will be a site at Brough in Yorkshire and at RAF bases in Marham, Norfolk, and Leeming in Yorkshire.
About 375 jobs will go in BAE’s maritime support business, mainly affecting Portsmouth. Jobs will also go from the company’s cyber intelligence business in London and Guildford.
Unite assistant general secretary Steve Turner said: “These devastatingly shortsighted cuts will harm communities, jobs and skills.
“These are world-class workers with years of training and expertise which an additional four jobs rely upon in the supply chain.”
Shadow defence secretary Nia Griffith told MPs during an emergency Commons question yesterday that the government needs to come up with an urgent plan to save the jobs.
She suggested that orders for nine replacement Hawk aircraft for the Red Arrows could be brought forward.
BAE said in a statement that it is expecting more orders, including one from Qatar proposing to buy 24 Typhoons and six Hawks.
It added: “Negotiations are progressing to agree a contract with the government of Qatar, which, if secured, would sustain Typhoon production jobs, and manufacturing well into the next decade.”
The Campaign Against Arms Trade called for the workers’ skills to be “put to use in more positive and sustainable industries” — including renewable energy and low-carbon technologies.
Campaign spokesman Andrew Smith said: “BAE Typhoon jets are being used right now in the Saudi-led destruction of Yemen.
“This is why government support should be shifted to other industries rather than those that are dependent on war and conflict to make a profit.”
BAE Systems chief executive Charles Woodburn said that the culling of jobs is “necessary” so that the company becomes more “streamlined and delayered.”