__omtpagibility of using nuclear weapons as a naval-mine countermeasure. One of them, sponsored by the Naval Ordnance Laboratory was to determine the ranges at which typical stockpile bottom mines would be neutralized by a shallow-water burst. To set up the experiment, a total of 120 mines, consisting of mines MK-25-2, MK-39-0, MK-50-0, MK-52-1, MK-52-2, MK-52-3, and MK-52-6 were laid in the Eniwetok Lagoon, north of ground sero, af*a@istances of 1400 to 8100 ft. The operation of 23 of the mines (planted at distances greater than those at which damage was expected) was monitored during the shot by means of a system of internal recorders designed to begin recording when the mines were armed and to continue recording until the mines were recovered. The depth of water at the mine fleld varied between 120 and 150 ft. The results of the test indicate that: 1. At distances of less than 1600 f from ground zero for weapons comparable in yield to that of shot Umbrella, 100 per cent clearance of mines may be expected. 2. At distances between 1600 and 2000 ff, 67 per cent of the MK-252's suffered component damage sufficient to render the mines inoperative. 3. At distances between 2000 and 2800 ff, 43 per cent of the MK-~25- 2'a guffered component damage sufficient to render the mines inoperative. The Navy Mine Defense Laboratory was the sponsoring agency of the other project participating in underwater experimentation. The over-all objective of the project was to determine the feasibility of employing nuclear weapons for wide area mine clearance by influence means. The specific objectives of this project were to (1) measure and record the amplitude, duration, and extent of mine actuating influences (pressure, acoustic, and mag- netic) that may be generated at the sea bottom by the explosion of a low yield nuclear weapon in shallow water (approximately 150 ft depth); and (2) determine the reaction of certain instrumented naval mines to the influences generated. Three LCU instrumentation platforms were located at distances of 8300, 20,150, and 44,750 ft from the Umbrella surface zero. Instrumentation was provided to obtain the time-pressure history resulting from the shot, including pressure changes due to waves, swells, and the shock wave; the time history of the magnetic field changes; the time history of the sound pressure level, 2 cps to 40 ke; the time history of displacement of the bot- tom; the mine reaction, including such items as search coil output, plate voltage rise, pressure switch opening, fires, and "looks"; and correlation of all influence measurements and mine reactions with respect to time. From the Umbrella shot the following tentative conclusions were made: 1. The shot was not significantly effective in causing MK-25-0, MK-25- 2, MK-50-0, and MK-36-2 mines planted at the three instrumentation plat- forms to register fire actuations. 2. One magnetic look was received by each operative MK~-25-0 and MK-25-2 mine at Platforms 1 and 2. Those at Platform 3 received none. The magnetic looks occurred at.a time that would indicate that they probably resulted from ground motion or’ the effects of the water shock wave. 3. All MK-25-2 mines received looks as a result of pressure waves generated by the shot. , 4. Anticountermine actuations were recorded for nine acoustic mines. A fire actuation was recorded for one. Based on the time of occurrence, it is probable that the ground-transmitted pressure waves were responsible for some, or all, of the actuations. 33