The US Air Force plans to order 100 planes of the B21 Stealth Bomber at $700 million each. This aircraft is made at Plant 21 in Palmdale, California. The development of this plane was kept hidden for seven years even to families with someone working at the plant. It is made by Northrop Grumman. The previous version of the plane was the B2 Spirit of which only 21 were made leading to a high cost of $2 billon per plane. These planes last for many years. The B52 bombers of the Vietnam era are still in use. Their cost is prohibitive for most countries. During the period after the collapse of the Soviet Union investment in these bombers declined. With new risks emerging for NATO in Europe and in Asia this aircraft is seen as an American deterrent.