Senior Full Stack Developer

GTMaritime; Warrington; Hybrid; GBP 90,000 - 120,000; Full time

Job summary

GTMaritime, part of the Valstone portfolio, is seeking a senior software engineer to own core backend features across distributed systems and the cloud. You’ll lead security-minded development for Replicate, Fastnet, and Deploy, review peers' code, and manage weekly release builds.

Based in Warrington with hybrid working, you’ll mentor teammates, fix complex production issues, and design robust end-to-end solutions. Maritime domain experience is not required; domain knowledge will be taught.

Qualifications

• 8+ years of commercial software development experience.
• Senior-level ownership of features end to end.
• Experience with large-scale distributed systems.

Responsibilities

• Own core backend features spanning remote agents, shore-side services and cloud stack.
• Diagnose distributed failures from logs and telemetry; deliver fixes to production.
• Review and authorize pull requests; manage weekly production release builds.
• Address security findings from penetration testing and ISO 27001 compliance.
• Mentor developers through pair programming and code reviews.
• Document build and deployment processes to avoid single points of failure.

Skills

C#/.NET expert

ASP.NET Core

Entity Framework Core

AWS in production

Distributed systems

Application security

CI/CD pipelines

Windows services/agents

Real-time messaging

TypeScript frontend

C++/legacy code

Maritime domain knowledge

Tools

SQL/MariaDB/MySQL

Git

Terraform/AWS tooling

Job description

Location: Hybrid (Warrington, United Kingdom)

Company: GTMaritime (Valstone Portfolio)

About the Company: GT Maritime provides mission-critical maritime cybersecurity and communications software to 2,000 companies and 16,000 vessels worldwide — roughly a quarter of the world's non-navy fleet. Based in Warrington, UK, GT Maritime operates as a focused, technically rigorous business with a strong culture of quality and long-term ownership. GT Maritime is part of the Valstone portfolio.

About Valstone: Valstone is an industrial software conglomerate that acquires and operates mission-critical software businesses across agriculture, logistics, food processing, bulk materials, and manufacturing. With 19 acquisitions completed across Canada, the USA, and the UK, Valstone takes a long-term, buy-and-hold approach — building businesses rather than exiting them. Valstone is part of the Valsef Group, a Montreal-based holding company. Sister entities include Valsoft (130+ acquisitions, $3B+ valuation), Permanent Corp, Valnet, and Valsef Capital.

Valstone at a Glance (Part of the Valsef Group)

• 4 core verticals
• Canada, USA and UK operations
• Buy and hold — no exit horizon
• $200M revenue target by 2026

Reporting to the Head of Engineering, this is a senior, hands‑on role with real authority attached: you'll own a core area of GT Maritime's platform end to end. When something breaks in production — a distributed fault with no clear cause, on equipment nobody can reach — you're the one who finds the actual root cause, builds the fix, and gets it safely shipped.

You'll own three products end to end: Replicate (file replication between ship and shore), Fastnet (packet transport and bandwidth management) and Deploy (software updates to vessel endpoints) — all C#, .NET and AWS. Beyond writing code, you'll hold pull request authority over other developers' work, own the weekly production release builds across the product estate, and carry the security and stability workload that comes out of penetration testing and ISO 27001.

We work Shape Up, in six‑week cycles — you get a problem and an appetite, not a spec, and you do the uphill investigation yourself before anything is built.

Design and build complex backend features spanning remote agents, shore‑side services and the cloud stack that connects them. Diagnose intermittent, distributed failures from logs and telemetry rather than guesswork, and own delivery end to end — test plan, edge cases, and rollback path included.

Act as a Change Authority: review and authorize pull requests from other developers as if you'd written the code yourself, including running it locally. Produce the weekly production release builds and verify rollback before every release.

Fix the security findings that come out of penetration testing — authorization defects, credential handling, secret management — and build to ISO 27001 requirements, producing the technical evidence the audit needs.

Mentor developers by pairing on hard problems and through review feedback that teaches. Document the build and deployment process so no part of the release depends on one person.

• Expert‑level commercial C# and .NET: advanced patterns, async and concurrency done correctly, performance and memory work
• ASP.NET Core Web APIs, Entity Framework Core, and long‑running Windows services or worker processes
• Real database depth — schema design, migrations, query optimization, index behavior and transaction isolation (MariaDB/MySQL, SQLite)
• AWS in production, not just in theory: Lambda, SQS, SNS, DynamoDB, S3, Secrets Manager, CloudWatch — able to debug a live issue from the logs
• Distributed systems instincts: retries, idempotency, eventual consistency, reconciling two systems that can't always reach each other
• Application security you can act on: authorization and access control, encryption and key management, credential storage
• Advanced Git and CI/CD pipelines; code review that catches architectural problems, not just style
• Around 8+ years of commercial software development, several at senior level owning features end to end
• Windows client/agent software: installers, services, code signing, upgrade and rollback
• Real‑time messaging (SignalR or equivalent), including tenant isolation
• Microsoft Graph, SharePoint or OneDrive integration experience
• Working TypeScript and modern front‑end knowledge, enough to finish a feature through the dashboard
• Comfort reading legacy code (C++, Visual Basic)
• AI‑assisted development experience (Claude Code, Amazon Q or similar) as everyday practice
• Maritime, satellite comms, or other bandwidth‑constrained domain background

We'd rather fix the cause than elevate the symptom. This is the engineer who independently takes a customer‑affecting problem, finds the actual root cause in a distributed system with intermittent faults, and gets the fix safely into production on equipment that’s difficult to reach. Maritime experience isn't required — we’ll teach you the domain.