Originally, the AN/SPY-3 active electronically scanned array primarily X band radar was to be married with Lockheed Martin's AN/SPY-4 S band volume search radar. Raytheon's X-band, active-array SPY-3 Multi-Function Radar (MFR) offers superior medium to high altitude performance over other radar bands, and its pencil beams give it an excellent ability to focus in on targets. SPY-3 will be the primary radar used for missile engagements. A 2005 report by Congress' investigative arm, the Government Accountability Office (GAO), questioned that the technology leap for the Dual Band Radar would be too much.