This paper presents the development and testing of a gamma radiation dose rate calculation model for the marine environment, and evaluates the potential use for such a model in both short term nuclear emergency response management and emergency response planning. This is believed to be the first implementation of a full field gamma radiation mapping model (including air attenuation and buildup) to be incorporated within a Lagrangian marine dispersion model. Calculated surface gamma ray dose rates for nine generic release scenarios are presented and used to undertake an emergency countermeasure optioneering assessment. •Novel gamma dose rate calculation tool for marine nuclear emergency response•Marine dose rate interpolation including water and air attenuation and buildup•Python based open-source development approach applicable to other dispersion models•Development of optioneering and short-term nuclear emergency response tools