The 40 year old E-2 Hawkeye radar aircraft passed a milestone this Summer, achieving a million flight hours. Introduced in 1964, the two engine, 24 ton E-2 was never produced in large quantities. The current models cost about $51 million each and are difficult to maintain. The E-2s always contained a large quantity of the most modern, and failure prone, electronics. Operating mostly off carriers, and thus constantly exposed to corrosive, salty ocean air, the aircraft take a beating. The five man crew are mostly concerned with using the large radar carried atop the aircraft, and keeping track of friendly, and hostile, aircraft and missiles at up to 400 kilometers distance. 

The aircraft can stay in the air for 4-6 hours at a time, and cruises at 450 kilometers an hour. The aircraft have had their electronics constantly upgraded over the years. Currently, the three system operators use large flat screen displays and many gigabytes of disk storage each (for capturing and comparing data). 

Each American aircraft carrier has four E-2s, and a total fleet of about 70 E-2s. There are several dozen in service in other countries, but only France operates them from carriers. Everyone else uses land bases. About half the E-2s ever built (production ceased in the 1990s) are still flying, and the United States expects to keep using them until 2020. After than, an unmanned aircraft will probably replace the E-2.