Washington, D.C. ? Boeing Co. on Monday announced a newly designed KC-767 as its proposed aircraft for a $40 billion Air Force contract competition to replace 179 refueling planes.

The Chicago-based company said at a news conference that it tweaked the design of its long-range 767 freighter plane to improve fuel efficiency and allow it to take off and land on shorter runways, giving it greater flexibility in combat situations.

Boeing is competing against Northrop Grumman Corp., which is expected to offer its KC-30, a modified Airbus A330, at a discounted price.

At stake for both competitors is a multiyear contract to replace a portion of the military’s older fleet of KC-135 aircraft, a medium-sized refueling plane made by Boeing. The $40 billion contract is the first installment of an expected three-phase deal that calls for more than 500 planes and could be worth an estimated $100 billion.