Job Description Engage in the early definition and development of complex Command & Control systems with ALTEN Ltd. Join our team as a Principal Systems Engineer, working at the very front end of the engineering lifecycle to define architectures, requirements and concepts from first principles. You’ll operate within uncertain and evolving domains, shaping system solutions for complex aerospace, land and maritime environments, while providing technical leadership and guidance across multidisciplinary engineering teams. Location: Berkshire On‑site: Hybrid, 3 days per week Seniority: Principal Security Clearance: Candidates must be willing and eligible to obtain SC clearance. Key Responsibilities Lead systems engineering activities across the full lifecycle, with strong focus on concept and early definition phases Define and develop system requirements and architectures within complex, evolving environments Conduct architecture and design trade studies, documenting options, risks and recommendations Scope and plan engineering activities across the full product lifecycle Produce high‑quality technical documentation and reports to support decision‑making Apply strong understanding of military communication systems and heterogeneous networks Perform system modelling using tools such as Enterprise Architect or Cameo Support networking and security function definition at system and sub‑system level Provide technical leadership, coaching and mentoring to less experienced engineers