Location: South West London Salary: £75,000 - £90,000 Clearance: SC (or eligible) As Principal Mechanical Engineer you will play a key role within the engineering team of a defence company based in London. You will act as a technical expert and lead in the development of electro‑mechanical products that are production‑ready, robust and compliant with industry standards. This role is suitable for Principal Mechanical Engineers, Mechanicals Leads or Senior Mechanical Engineers looking to step up. You will work on complex mission critical projects, applying your expertise in mechanical design, materials, manufacturing and regulatory standards. Requirements: * Significant experience in the defence, maritime or aerospace sector. * Strong knowledge of defence mechanical design standards and regulations. * Ability to lead design from concept through manufacture. * Security Clearance: due to the nature the work, you MUST be a British Citizen without dual nationality...