The CHURCH OPAL Exercise is one of a series of LRAPP Exercises designed specifically to acquire environmental acoustic data required for ASW program decisions. At-sea operations were conducted during September 1975 in a region of the Northeast Pacific Ocean. This exercise includes the following ocean acoustic experiments related to the Moored Surveillance System MSS, the Sound Surveillance System SOSUS, and the Surveillance Towed Array Sonar System SURTASS 1 Noise Floor Characteristics, 2 ASEPS Evaluation Coherent Multi Array Processing, 3 Horizontal Directionality of Ambient Noise Towed Array Performance. The objective of the Noise Floor Verification Experiment is to verify the noise floor concept. The noise floor is a depth below which distance shipping noise is significantly reduced and where short range acoustic sensors could attain a substantial performance gain.