Job Title: Principal Mechanical Design Engineer Job Location: Barrow-in-Furness, Hybrid We offer a range of hybrid and flexible working arrangements please speak to your recruiter about the options for this particular role Salary: Circa £55,000 Who we are: Join BAE Systems and youll be part of something bigger. As a valued member of our global colleague network, youll bring your unique skills and perspectives to help pioneer progress and protect what matters most. Youll be trusted to play your part in delivering the advanced, technology-led defence, aerospace and security solutions of tomorrow shaping a safer future, for all of us. What you will be doing: In this role, you will lead the development of complex mechanical fluid systems that support critical submarine platform functions. You will define system requirements, develop high-integrity engineering solutions and ensure designs meet demanding performance, safety and environmental requirements. Working closely with engineering and project teams, you will support modelling and analysis activities, technical reviews, and supplier engagement while contributing to cost estimation, risk assessments and the resolution of technical challenges across the programme. Core Duties: Lead the end-to-end design and development of complex fluid systems for submarine platforms, ensuring solutions meet demanding operational, safety and environmental requirements. Produce and review high-value engineering deliverables including schematics, P&IDs, engineering calculations, system descriptions and 3D models. Carry out advanced system analyses including flow, pressure, thermal and transient modelling to validate performance under challenging operating conditions. Select and assess critical equipment such as pumps, compressors, valves, heat exchangers, filters and tanks, ensuring suitability for submarine environments. Review supplier documentation to ensure compliance with requirements relating to shock, vibration, temperature, atmosphere, maintainability and equipment accessibility. Contribute to technical reviews, hazard studies and verification activities to ensure design quality, safety and regulatory compliance. Support resolution of technical issues, design modifications and non-conformances across the engineering lifecycle. Hold a relevant engineering degree and strong experience in mechanical, marine, process or fluid systems engineering within complex or regulated environments, with knowledge of fluid dynamics, thermodynamics and system performance modelling; experience with tools such as FloMASTER, FluidFlow, MATLAB, CFD or ANSYS is desirable. The Mechanical Engineering Discipline Team: This is an exciting opportunity to join the SSN-AUKUS Platform Mechanical Integrated Delivery Team as a Principal Mechanical Design Engineer, acting as a technical specialist for critical compressible and incompressible fluid systems essential to submarine operations. You will take ownership of high-integrity mechanical designs in one of the most demanding engineering environments, working across multidisciplinary teams to develop complex system solutions, influence platform-level decisions and ensure designs meet strict safety, performance and environmental standards. This role offers the chance to contribute directly to one of the UKs most advanced defence programmes. Relocation support may be available for submarine roles, subject to eligibility criteria. Why BAE Systems? Here youll build a career with purpose and limitless possibilities. With lifelong learning and meaningful work this is a place where you can grow your career with confidence and be empowered to be your best.?Youll be recognised for your contribution and enjoy rewards tailored to whats most important to you and your family support for your financial and personal wellbeing, as well as a balanced lifestyle. In an environment embracing sustainable ways of working and with a strong sense of shared purpose, our supportive culture is a place you can feel you belong and proud of the difference you make. A place where everyone can thrive. Were committed to building an inclusive workplace where everyone feels valued and supported. We know that a diversity of backgrounds, perspectives and experiences strengthens our teams and is vital to the work we do. We welcome applications from all candidates and give full, fair and open consideration to everyone. If you require any reasonable adjustments during the recruitment process, please contact our recruitment team to discuss any further support you may need. Connect with us at baesystems.com/connect Security Statement: Please be aware that many roles at BAE Systems are subject to both security and export control restrictions. These restrictions mean that factors such as your nationality, any nationalities you may have previously held, and your place of birth can restrict the roles you are eligible to perform within the organisation. All applicants must as a minimum achieve Baseline Personnel Security Standard. Many roles also require higher levels of National Security Vetting where applicants must typically have 5 to 10 years of continuous residency in the UK depending on the vetting level required for the role, to allow for meaningful security vetting checks. Closing Date: 27th March 2026. We reserve the right to close this vacancy early if we receive sufficient applications for the role. Therefore, if you are interested, please submit your application as early as possible. LI-MS1 LI-Hybrid