Bremont Supermarine 300M: A Modern Diver on Brown Leather

A diver on brown leather proposes a different life from one on a wetsuit strap. The Bremont Supermarine 300M in this configuration looks ready for an ordinary day with a jacket and jeans, while retaining the case and timing bezel of a water-oriented sports watch.

Reference SM40-ND-SS-BL-L-S pairs a blue gradient dial with brown leather and no date. It belongs to the redesigned Supermarine range, using a 904L steel case and a 50-hour movement. The buying question is whether this modern interpretation gives you a distinctive everyday watch, rather than whether the name alone recalls a Bremont you admired several years ago.

Based on Bremont’s published information. Specifications checked on 8 September 2026.

The exact reference

Specification source: Bremont UK Supermarine 300M exact blue leather reference.

An aviation name on a diving watch

Bremont’s account of the Supermarine’s origins identifies the 43 mm Supermarine 500 of 2009 as its first diving watch. The name honoured the British aircraft manufacturer associated with the S6B seaplane and Spitfire, connecting the collection to the founders’ aviation interests even as it entered the water. The range subsequently developed smaller and differently styled models. Today’s 300M is a redesigned interpretation, with a different case silhouette and material specification from older Supermarines. That history is useful when browsing the name across generations: a shared aviation reference does not imply unchanged construction. The present watch should be judged as its own design, retaining the broad sporting idea while offering a more contemporary case and dial arrangement.

The redesigned case is the first thing to understand

Bremont specifies 904L stainless steel and a symmetrical outline with protection around the crown and bezel. The 40 mm diameter sounds moderate, but the 49 mm case length gives it a meaningful span along the wrist. At 12 mm thick, it has enough height to remain visibly a sports watch.

That combination deserves a proper fitting assessment. Someone with a broad, relatively flat wrist may welcome the elongated outline. Someone who already finds long lugs troublesome should pay more attention to the 49 mm length than the appealingly familiar diameter.

The published 75 g figure is for the watch head only. It should not be compared directly with the total weight of a competitor on a steel bracelet. The leather configuration will feel different from a bracelet model, but a fair comparison begins by checking what each manufacturer has actually weighed.

The dial is stronger without a date

The blue gradient gives the face visual depth, while applied markers and broad hands establish a clear time display. Without a calendar window, the arrangement stays balanced around the centre. That suits a watch whose bezel and case already provide plenty of structural detail.

The blue aluminium bezel continues the colour outward. Its trapezoid markings align visually with the dial’s main axes, giving the front a more deliberate geometry than a plain minute ring. The result is recognisably sporting without depending on a black dial or aged-looking colour palette.

Aluminium is the actual insert material here, not ceramic. That is part of the reference’s specification rather than a flaw to explain away. Decide whether the combination of colour, finish and case shape appeals enough to justify the watch at its current price.

The strap is a style choice with practical consequences

The brown leather strap uses quick release and a pin buckle. It is a natural partner for the blue dial if you want the watch to work with casual jackets and less technical clothing. The stitching reinforces that softer appearance.

Bremont lists the standard strap for wrists from 16.5 cm to 22 cm. If your wrist falls outside that range, establish the appropriate strap option before ordering. A well-sized case does not solve a strap that cannot close at the position you want.

The 300 m rating describes the watch case’s water capability. Leather makes this particular configuration more compelling for everyday dry wear than for repeated swimming. If regular water use is the plan, consider the manufacturer’s rubber or bracelet options and compare the complete reference and price.

The movement suits a daily routine

The modified BE-92AO has a 50-hour reserve. From full wind, it offers more than two days of running time, making an occasional day off the wrist manageable. A full Friday-to-Monday break can still exceed that capacity, so it is not the same ownership proposition as an 80-hour movement.

The closed caseback carries an engraved map of the oceans. It keeps the rear focused on the collection’s theme rather than displaying the mechanism. Whether that is appealing depends on what you enjoy about mechanical watches: the subject and overall design may matter more than seeing the rotor.

The three-hand layout also simplifies restarting the watch. There is no date to align after a long rest. For someone who wants an uncomplicated mechanical diver with a distinctive face, that restraint is a useful part of the package.

The comparison worth making

The 40 mm Christopher Ward C60 Trident Pro 300 offers a ceramic bezel, a shorter 47.45 mm lug-to-lug span and an 11.3 mm case. It is a sensible alternative to try if you like the blue-diver idea but want different proportions and a bracelet-focused configuration.

The Bremont’s argument is its particular case, no-date dial and leather presentation. At £3,100 on the UK site on 8 September 2026, those qualities should be what you want to pay for. The material name alone cannot decide the value of the complete watch.

Who should choose this Supermarine?

Choose it if you want a substantial modern diver that looks at home on leather, the 49 mm length fits well, and the uncluttered blue dial is the attraction. It offers a recognisable alternative to the familiar black sports-watch formula.

Choose a different configuration for frequent swimming, or a shorter case if fit is marginal. This Supermarine is most persuasive when its everyday styling is the reason you reach for it, with the diving hardware supporting that role rather than dominating the story.

Image: AI-generated editorial illustration of Bremont SM40-ND-SS-BL-L-S. Design details are approximate; this is not a product photograph.