BAE Systems is to axe 600 jobs at two factories in northern England, following the completion and delivery of current orders.
The firm says 450 jobs will disappear at Brough, near Hull, home of the Hawk aircraft and 134 will go at Woodford, the home of Nimrod.
The cuts will affect engineering, manufacturing and business support.
Workers' union Unite says it is shocked at the scale of the cutbacks and will fight any compulsory redundancies.
National officer Bernie Hamilton says Unite will be working with management to find alternatives including re-skilling, transfers to other operations and work packages from other projects.
"We have known for some time that we had a challenge on our hands at both sites due to the completion and delivery of current orders for the Fast Jet Trainer and the completion of work cycles at Woodford," Hamilton says.
"Winning new orders in a competitive market is very challenging.
"At the same time the industry is rising to meet demand for new technologies like the Unmanned Combat Aircraft.
"In the long-term it is imperative that the aerospace industry and the UK Government reaches agreement to safeguard the UK's large fixed wing capability for future generations," he says.
By Elizabeth Clifford-Marsh