The Apollo project will mature and demonstrate in operational environment, the disruptive installation of a dual fuel ammonia engine in an offshore supply vessel to ammonia operation reducing emissions by 70%. The project is developed to closely answer the HORIZON-CL5-2022-D5-01-04 topic of transformation of the existing fleet towards greener operations through retrofitting (ZEWT Partnership). The specific objectives include: 1) Successful large-scale demonstration of the use of dual-fuel ICE (ammonia-based) in an existing vessel; 2) Complete first classification under DNV “Gas fuelled, Ammonia”; 3) 70% reduction of CO2 emissions and NOx emissions below 2.4 g/kWh from vessel operations; 4) Complete retrofitting solution to operate on ammonia, through development of safe ammonia storage and operation, including both deck load or below deck tanks; 5) Demonstrate the retrofit in replicators in other two vessels with different use (dredging and offshore construction) and validate feasibility for scaling; 6) Support to the expansion of the ammonia bunkering network in the North Sea and beyond, obtain 100% green ammonia for the project’s needs; 7) Validated business case for ammonia as a ship fuel with operational expenditures <130% from baseline by project end. The Apollo solution will be flexible, so ship owners, ship designers, shipyards, classification agencies and insurance companies can quickly adopt it into their decision-making processes. The consortium will prepare the business case for ammonia in the waterborne transport sector, from the production of green ammonia to its use in different ships on the European scale.