The primary purpose of the explosion tests described was to inform the Seacoast Service Test Section, Army Ground Forces Board No. 1, of the effectiveness of large cast TNT submarine mines after extended exposure to sea water Army Project SA 547. A secondary purpose, of interest to the authors, was the study of the application of crusher-gauge theory in explosions of large charges. Three mines were detonated. Shot 1 was a dry mine exploded as a standard for later comparison. Shots 2 and 3 were wet mines, in which the charges had been exposed to sea water for several months by removing the two top covers from each mine and submerging. Comparison of the explosive forces was made by the effect on 32 ball crusher gauges placed at ranges varying from 75.5 to 157.8 feet. The effectiveness of the wet mines was found to be about 6 per cent and 5 per cent higher than that of the dry mine but this slight apparent improvement, due to exposure, was not found to be statistically significant. Theory proposed by G. K. Hartmann on action of crusher gauges permitted absolute peak pressures to be computed. These agreed satisfactorily with pressures expected from purely theoretical calculations. Author.