## 5 Conclusions  
This article presented a way to design a digital twin to represent supply chains for cyber exercises. The development of a digital twin of a food supply chain for cyber exercises (RQ1) could be achieved with standard web technologies. The design of a food supply chain digital twin uses generic apparatus services to simulate various production machines. In addition, the raw material system and the end storage can be simulated with databases and queues. Standard web technologies are sufficient to build the services required by a digital twin for cyber exercises. Accordingly, the developed simulation concept for the food supply chain (RQ2) followed a web service architecture. The use of simulated parts of the food supply chain actors, such as MES and SCADA, facilitates the immersiveness of the exercise. In addition, the scalable apparatus architecture makes it feasible to create new scenarios and extend the existing ones, depending on the domain needs.  
Digital modeling and twinning can be seen as valuable tools for exercises. When building digital twins, a restricted domain and application area, e.g., cyber security, serve to constrain the complexity of the system. However, the evaluation of such constructs could be difficult because of the specifics of the domain. The realistic nature of the scenario is essential to cyber exercises. The simulated products were dynamically created as a process which enabled unusual events during the exercise. Cyber attacks against such targets are sensible for the attackers (RT) and for the exercise, because the consequences affect a realistic process.  
The main limitation of this study is that the system was built for one specific cyber range, the RGCE. The solutions used in this cyber range could be idiosyncratic to it, and adaptability to other environments might be inconvenient. Secondly, as this is the first iteration of this kind of digital twin approach, the design and development process of future digital twins might reveal better technical practices in the implementation.  
The use of digital twins of domain systems as part of cyber exercises improves the immersiveness by simulating real supply chains. This way, the participants can exercise in a realistic environment which mirrors the systems and processes in their ordinary work. Implementing the digital twin requires a modular design with appropriate messaging simulating the real-world counterparts. Further research includes detailed validation by analyzing the conducted cyber exercises. The generalizability of the solution could also be studied.  
Conceptualization, M.P., K.-E.R., K.P., E.J. and T.K. ([PERSON]); methodology, M.P., K.-E.R., K.P., E.J. and T.K. ([PERSON]); software, M.P., K.-E.R., K.P., E.J. and T.K. ([PERSON]); investigation, T.S. and T.K. ([PERSON]); resources, T.K. ([PERSON]); writing--original draft preparation, T.S. and T.K. ([PERSON]); writing--review and editing, T.S., [PERSON] ([PERSON]) and M.P.; visualization, M.P. and T.S.; supervision, [PERSON] ([PERSON]); project administration, [PERSON] ([PERSON]) and [PERSON]; funding acquisition, [PERSON] ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
This research and the APC were funded by the Regional Council of Central Finland/Council of Tampere Region with fund of Leverage from the EU, European Regional Development Fund (ERDF) and Recovery Assistance for Cohesion and the Territories of Europe (REACT-EU) Instrument as part of the European Union's response to the COVID-19 pandemic, as part of the Food Chain Cyber Resilience project of Jamk University of Applied Sciences Institute of Information Technology (grant number A77620).  
Data Availability Statement: Data sharing not applicable.  
The authors would like to thank project manager [PERSON] for assistance with project data and [PERSON] for proofreading the manuscript.  
The authors declare no conflict of interest.