The Naval Civil Engineering Laboratory (NECEL) has developed and tested a series of experimental valves varying in capacity from 700 cfm to 10,000 cfm with 1.0 inch of water-flow resistance. A 2,500-cfm valve evolved after a series of tests with the 700-CFM Buckling Plate Valve. Although the configuration of the larger valve differed from its predecessor, the consept remained essentially unchanged. Experimental work with the 2,500-CFM Valve Module inicated that a pressure balance across the piston caused the shock catcher to be ineffectual, particularly at low overpressures. Remedial measures included decreasing piston clearance, installing a 0-ring seal, and venting the downstream end of the shock-catcher barrel. Following a series successful tests, a 10,000-CFM High Capacity Valve, which consisted of four 2,500-cfm valves in a parallel arrangement within the same housing, was designed and fabricated. The valve was field tested at Operations PRAIRIE FLAT with exellent performance results. The valve closed in 15 msec without damage from the external environment.