The current article describes the basics and prospects of the ultrasound-assisted cleaning of shell and tube heat exchangers that are used, e.g., on ships. A main issue of seawater heat exchangers is their clogging. After a certain operating time, the fouling process (barnacles, algae, etc.) starts, which results in a decreased performance that produces a noticeably reduced flow rate and a declining transmission of heat energy. Based on the current state of the art, heat exchangers are cleaned by mechanical or chemical (CIP, cleaning in place) methods. Especially on ship-based systems, a mechanical cleaning in very narrow spaces can be difficult and the usage of chemicals for CIP may generally be prohibited. An ultrasound-assisted cleaning would significantly save time and manning. Based on previous experiments, a test reactor represented by a shell and tube heat exchanger with ultrasound-assisted cleaning has been designed. A FEM (finite element method) simulation is performed to provide information about the ultrasound power distribution inside the reactor. Further, the assembly and commissioning of the test reactor with associated comparative measurements were carried out, which are also reported here.