Principal Mechanical Engineer

Addition; London Borough of Richmond upon Thames; Hybrid; GBP 120,000 - 138,000; Full time

Job summary

Addition is seeking a Principal Mechanical Engineer to lead mechanical design across defence programmes in a hands‑on leadership role. You will drive FEA, thermal/CFD analyses and ensure designs meet defence standards and programme deadlines.

You’ll mentor engineers, produce documentation and BOMs, manage risks, and liaise with customers, suppliers and test houses while acting as Design Authority when required. Eligibility for UK security clearance is required.

Qualifications

• Experience in mechanical design engineering, ideally within a complex engineering or defence environment.
• Degree in Mechanical Engineering or a related discipline, or equivalent practical experience.
• Experience with CAD tools, ideally Creo or similar.

Responsibilities

• Lead mechanical and electro‑mechanical design activities across one or more programmes.
• Conduct and review FEA and thermal/CFD analysis to validate and justify designs.
• Approve mechanical designs, acting as Design Authority when required.
• Resolve mechanical engineering issues throughout design, manufacture, integration, testing and qualification.
• Produce, review and approve technical documentation, including engineering drawings, specifications and Bills of Materials (BOMs).
• Ensure compliance with applicable defence standards, engineering processes and configuration management requirements.
• Provide technical leadership, mentoring and guidance to mechanical engineers.
• Liaise with customers, suppliers, manufacturers and test houses.
• Manage design risks, technical queries, requirements and engineering changes.
• Extensive experience in mechanical design engineering, ideally within a complex engineering or defence environment.
• Current SC security clearance or eligibility to obtain it.
• Naval defence programmes, particularly Platform Management Systems (PMS) for surface or submarine platforms.
• Experience with shock, vibration, EMC and climatic testing.
• Experience supporting hardware development, integration and qualification.

Skills

FEA analysis

Thermal CFD

Design Authority

Technical leadership

Problem solving

Education

Mechanical Engineering degree

Tools

Creo CAD

Job description

Contract | 6 Months+ | Inside IR35 | Very Competitive Day Rate

Hybrid – South West London

The Opportunity

We’re seeking an experienced Principal Mechanical Engineer to lead mechanical design activities across complex defence engineering programmes.

This is a hands‑on technical leadership role, combining mechanical design, Finite Element Analysis (FEA), thermal analysis/CFD and design approval. You’ll act as a mechanical engineering subject matter expert, ensuring designs meet technical requirements, defence standards and programme deadlines.

You’ll also provide technical leadership to the mechanical team, support hardware development and qualification, and work closely with customers, suppliers and manufacturers.

Key Responsibilities

• Lead mechanical and electro‑mechanical design activities across one or more programmes.
• Conduct and review FEA and thermal/CFD analysis to validate and justify designs.
• Approve mechanical designs, acting as Design Authority when required.
• Resolve mechanical engineering issues throughout design, manufacture, integration, testing and qualification.
• Produce, review and approve technical documentation, including engineering drawings, specifications and Bills of Materials (BOMs).
• Ensure compliance with applicable defence standards, engineering processes and configuration management requirements.
• Provide technical leadership, mentoring and guidance to mechanical engineers.
• Liaise with customers, suppliers, manufacturers and test houses.
• Manage design risks, technical queries, requirements and engineering changes.
• Extensive experience in mechanical design engineering, ideally within a complex engineering or defence environment.
• Degree in Mechanical Engineering or a related discipline, or equivalent practical experience.
• Experience with CAD tools, ideally Creo or similar.
• Understanding of relevant defence standards and engineering processes.
• Ability to work independently, lead technical activities and manage competing priorities.
• Current SC security clearance or eligibility to obtain it.
• Naval defence programmes, particularly Platform Management Systems (PMS) for surface or submarine platforms.
• Experience with shock, vibration, EMC and climatic testing.
• Experience supporting hardware development, integration and qualification.

If you’re an experienced mechanical engineering professional looking for a technically challenging contract with real ownership of design decisions, we’d like to hear from you.