Keeping a submarine stable underwater is important to be able to execute missions. Therefore, one of the main systems on board of submarines is therefore the ballast trim system. This system is able to maintain the submarine balanced. There must be equilibrium in weight and buoyancy as well as in the trimming moment. This makes the ballast trim system a vital system on board of submarines. The world around us changes, causing new mission specifications and requirements. This results in a different operational profile than before, which has consequences for the ballast trim system. For example, for a modern submarine hovering is desired, resulting in a faster and more accurate ballast trim system. Therefore, the existing systems must be reconsidered for modern SSK submarine applications. Next to the changed environment, new technologies are available, which might be applicable for a modern SSK submarine. The main goals of this research are: give insight in the ballast trim system and see which technologies are best to use in the ballast trim system. The technologies are tested on the 4000 and 2000 ton BB2 submarine. In this research different empirical models were set up in order to simulate the behaviour of the different ballast trim systems. The results of these models are compared to each other based on energy, noise and redundancy. As an input, different mission profiles were made, which are likely to be executed by a modern SSK submarine. The ballast trim system was divided into three separate systems for the comparison, namely: trim, compensation and hover. From the simulation made there was seen which modelled solutions were the best capable to use as a ballast trim system. In this research also the second order effects of waves were included. There is seen from the simulation that it is possible to compensate for the motions due to these second order wave effects. The simulations also showed that a new technique, the so called ‘variable buoyancy system’ is very promising. With the results from this research it can be seen which system can be best used as ballast trim system for the three different tasks on board of the BB2 submarine. To maintain longitudinal equilibrium, it is best to use a centrifugal pump to transfer ballast water between tanks. To maintain balance between the weight and buoyancy forces of the submarine, it is best to use a plunger pump. It is also seen that a centrifugal pump in a system with a very large static head compared to dynamic head, is hard to operate and can even become incapable of expelling water from the tank. For hovering, a special dedicated system is needed. For the 4000 ton BB2 submarine, it is best to use a pre-pressurised tank to lose weight very fast in case of a change in seawater density. The 2000 ton BB2 submarine can use its snorkel mast to maintain equilibrium. For low frequency forces such as the second order forces due to waves, both studied BB2 submarines can use their snorkel mast to keep the submarine at depth.