Ballistic Missile Early Warning System
（重定向自BMEWS）
4628.png"){kind=spacer}
![4 AN/FPS-50 detection reflectors at Thule J-site (replacement by an AN/FPS-120 with](/Images/godic/202501/01/Thule_BMEWS4628.jpg")
![The Thule J-site BMEWS station's detection arcs of 200°[43] were a missile warning](/Images/godic/202501/01/1961_Eyes_of_the_North_-_minute_4-51_--_BMEWS_arcs_and_Q_points4628.png")
The RCA 474L Ballistic Missile Early Warning System (BMEWS, "474L System", Project 474L) was a USAF "Big L" Cold War system of radar, computer, and communications systems that included the first operational ballistic missile detection radar. The network of 12 radars for detecting "a mass ballistic missile attack launched on northern approaches [for] 15 to 25 minutes warning time" also provided Project Space Track satellite data (e.g., about 1/4 of SPADATS observations).