Many active and former military installations have ranges and training areas that include adjacent water environments such as ponds, lakes, rivers, estuaries, and coastal ocean areas. Munitions were fired or disposed of using various methods at numerous underwater sites. The sites containing underwater munitions include ranges and target areas with a variety of surface and subsurface munitions, defense sites including forts and coastal artillery batteries, ocean disposal operations prior to 1972, acts of war such as combat sites or sunken vessels, accident sites, and former manufacturing and handling sites for military munitions and open burning/open detonation (OB/OD) practices. Ranges and targets include coastal defense sites, island targets, ranges that were previously land targets and were flooded, and littoral training areas. SERDP and ESTCP hosted a meeting on Monday, November 30, 2009, to assess the status of various elements needed to evaluate risk associated with munitions in the underwater environment. The main objective of this meeting was to evaluate the adequacy of modeling capability and data sources needed to make defensible risk-based decisions regarding underwater munitions. Elements of interest include: Mobility of Munitions, Corrosion, Release Rate, Fate and Transport, and Ecotoxicity. This report describes the current state of the science and knowledge gaps for each of these elements.