Status: Study 1960.
The principle was that the submarine could take a position under the path of the satellite. As it passed overhead, a Polaris missile would be launched with a peak altitude close to that of the target. The ASAT used a restartable upper stage to 'hover' for up to 90 seconds awaiting the satellite. An optical homing system would first locate, then track the target satellite. A data link was provided to the submarine for control. Once committed, the ASAT would put itself on a collision course with the target. A proximity fuse would detonate a warhead with thousands of steel pellets. To assure a kill, more than one ASAT could be launched simultaneously by the submarine.
Early Spring was first presented to Congress in March 1961. By 1964 several alternate configurations were evaluated, and by the late 1960's the optical tracker was showing good results in tests. The project was officially cancelled in the late 1960's. However the same concept can be found in the Navy's manned Space Cruiser concepts of the early 1970's and 1980's. And in 1978 the Joint Chiefs of Staff directed that work began on a "low-risk ASAT system using off-the-shelf technology..... employing pellets as its kill mechanism...." which may indicate the original system went operational and black.
Early Spring was a conventional ASAT launched by Polaris missiles from US Navy ballistic missile submarines. As an enemy satellite passed overhead, a Polaris missile would be launched. The ASAT used a restartable upper stage to 'hover' in front of the oncoming satellite. An optical homing system would first locate, track the target satellite, and then ASAT would put itself on a collision course with the target. A proximity fuse would detonate a warhead with thousands of steel pellets.