Workers in Calgary, Ottawa and Halifax were advised as early as October 2009 that there would be workforce reductions during the next 18 months, with layoffs coming in periodic waves since then, said Amy MacLeod, a spokesperson for the firm.
She said the layoffs were part of the cyclical nature of the defence industry and are expected as a normal way of doing business.
"The nature of our business is such that we have very long-term programs that develop under a number of years," she said.
"We're adjusting business resources to align with the current business needs, as they happen."
GD had 2,000 Canadian employees in October 2009 and after Monday's layoff has around 1,460. Individual office reductions are not being released, but there are currently around 1,100 in Ottawa.
GD integrates defence systems for land, air and sea applications for customers ranging from the United Kingdom army to the Swedish navy.