A previous paper has shown an interesting structure for the optimum array‐processing system using long observation time to detect weak stationary Gaussian signal in stationary Gaussian noise fields. For dominant amplifier and system noise (Case I discussed by Middleton and Groginsky), this structure is “factored.” The previous result is generalized to linear nonidentical hydrophones. A valid procedure for finding causal optimum filters is presented. The results are extended to the case or known signal; the optimum filters are not matched to the signal, but to a waveform dependent on signal, noise, and array structure.