Northrop Grumman, the US’s third-largest defence group, said on Tuesday it had made a net loss of $2.5bn in the fourth quarter of 2008 after writing down the value of acquisitions it made several years previously.

The Los Angeles-based company had warned last month that the fall in equity markets last year had prompted it to take a $3.1bn charge in the fourth quarter after writing down the book value of businesses it took over in 2001 and 2002 which are now part of its shipbuilding and space units.