The Apollo project will demonstrate the conversion of dual fuel engines to operate on ammonia as fuel by retrofitting an existing offshore vessel. We will redesign the dual fuel main engines of the platform supply vessel Viking Prince owned by Eidesvik to run on 70% ammonia, which will contribute to a 70% reduction in greenhouse gas emissions (3180 tonnes of carbon dioxide/year) compared to the current engine. To ensure that our solution is as safe or safer than existing systems, safety will be a central aspect of all development and execution phases of Apollo. We will also demonstrate retrofitting on other types of vessels and on inland operating environment through simulations. There are three major innovation areas associated with the project: 1) Installation of new green technology on existing tonnage / ships, 2) technical integration with existing energy systems on board and 3) development of internal combustion engine technology. The innovation will bring about a climate-friendly solution that can be realized in commercial shipping in the shortest possible time with an acceptable risk. The project aims to increase the TRL level of the solution from 6 to 8-9 and achieve full-scale demonstration of ammonia combustion engines in the vessel Viking Prince. The use of carbon-free fuels such as ammonia in internal combustion engines will be an important next step in the development and a "game changer" for energy systems in ships in terms of reductions in emissions. The use of a dual fuel solution also provides benefits for a number of ship types in the form of fuel flexibility and the possibility of zero-emission operations in vulnerable areas, or where cleaner fuel is available in the future.