Case Study: Precision Machining of Submarine Hatch Sealing Surfaces

Client: BAE Systems
Industry: Defence / Submarine Manufacturing
Application: Pressure-Rated Hatch Sealing

The Challenge

Reekie Machining was approached by BAE Systems, one of the world’s leading submarine manufacturers, to support a highly specialised machining requirement that could not be completed by their incumbent supplier.

The task involved machining a large submarine hatch coaming to incorporate a precision O-ring sealing groove capable of maintaining a reliable seal at operating depths of up to 600 metres. Both the sealing face and groove geometry were critical to the performance and safety of the hatch.

Key challenges included:

• A continuous inverse dovetail O-ring groove, running around a 6.0 m × 1.2 m hatch

• Large radii in each corner, requiring uninterrupted accuracy

• A groove width of just 8 mm, demanding extremely precise tooling

• A required surface finish of Ra 0.8 µm for sealing integrity

• All machining to be carried out inside a partially constructed submarine, within narrow compartments and with minimal clearance around the hatch

The Solution

Reekie Machining developed a bespoke CNC milling solution capable of machining both the hatch sealing face and inverse dovetail groove in a single setup, eliminating the risk of misalignment and ensuring dimensional continuity around the full perimeter.

To achieve the required groove profile and surface finish, Reekie worked closely with a specialist tooling partner to design and manufacture custom dovetail cutting tools tailored to the 8 mm groove width and finish specification.

Recognising the criticality of the work and the tight on-site schedule, Reekie carried out a full mock-up and trial machining process at its own facility prior to mobilisation. This allowed the machining strategy, tooling, and parameters to be fully optimised, reducing risk and ensuring predictable performance once on site.

Delivery

The bespoke CNC milling equipment was successfully installed within the confined submarine compartment, despite extremely limited working space. The hatch coaming was machined precisely to specification, achieving the required geometry and surface finish throughout.

All work was completed on time and in full compliance with the client’s technical requirements.

The Result

• Precision O-ring groove and sealing face machined in situ

• Surface finish achieved to Ra 0.8 µm

• Continuous, accurate geometry around the full hatch perimeter

• Critical programme milestones protected

• Client requirements exceeded in a highly demanding environment

Why Reekie Machining

This project demonstrates Reekie Machining’s ability to:

• Deliver bespoke machining solutions where standard approaches are not viable

• Operate in confined, high-risk, and safety-critical environments

• Design and manufacture specialist tooling for extreme precision

• Reduce project risk through detailed planning and off-site proving