The Tudor North Flag (reference M91210N) is a 40 mm stainless steel sports watch built around the MT5621, the first movement Tudor made entirely in house. It shows its roughly 70-hour power reserve on a dial window at 9 o'clock, a date at 3 o'clock, and a skeleton-style structure of bold numerals and indices that reads as a tool watch rather than a diver. This guide covers what the watch is, what the movement does, how it differs from the Black Bay, Ranger and Pelagos, and who should look for one. Bizak & Co. is a sourcing desk, so every North Flag is found to order rather than held in stock.
Last reviewed on October 28, 2026 by Filip Biczak. Specifications come from Tudor's own launch material and published reviews; Tudor has since reshuffled its range, so confirm current catalogue status with an authorised retailer. Sources: Tudor and COSC.
What is the Tudor North Flag?
The North Flag is Tudor's 40 mm steel explorer-style watch, introduced in 2015 as the first Tudor with an in-house movement. Tudor promoted it with the story of the 1952 to 1954 British North Greenland Expedition, whose members wore Tudor Oyster Prince watches, a link that places the North Flag in Tudor's expedition heritage. Unlike the Black Bay, it has no rotating bezel: the case is a smooth, brushed 40 mm cylinder with a screw-down crown, a sapphire crystal and a dial that puts legibility first. The steel M91210N is the model most buyers mean when they search for the name.
Which movement does the North Flag use?
The North Flag runs the MT5621, Tudor's first movement built entirely in house, rather than a modified third-party base. It is a self-winding calibre with a silicon balance spring, a variable-inertia balance and about 70 hours of power reserve. It is certified as a chronometer by the independent Swiss institute COSC, which tests the movement for accuracy before it is cased. The 70 hours matter in practice: a North Flag taken off on Friday evening is still running on Monday morning, which was well beyond the 40 to 48 hours common in automatic watches when it launched.
How does the power reserve indicator work?
The power reserve indicator is a small dial at 9 o'clock that shows how much running time is left in the mainspring. Its needle moves across a scale as the watch winds and unwinds, so you can see at a glance whether the watch will last the night or needs a wind. The same window is the design signature of the watch: it breaks the symmetry of the dial and gives the North Flag a character that other Tudor sports models, which keep a clean dial, do not have. Some owners find it busy, while others consider it the reason to buy the watch.
North Flag specifications
| Attribute | Tudor North Flag M91210N |
|---|---|
| Introduced | 2015 |
| Case | 40 mm stainless steel, brushed, screw-down crown |
| Movement | MT5621, in house, automatic |
| Power reserve | About 70 hours, shown on a dial indicator at 9 o'clock |
| Certification | COSC chronometer |
| Functions | Hours, minutes, seconds, date at 3 o'clock, power reserve |
| Water resistance | 100 m |
| Crystal | Sapphire |
| Bezel | Fixed (non-rotating) |
Straps vary by listing: leather and steel bracelet versions have both been offered, and a fabric strap pairs well with the black dial. See the Tudor North Flag collection for the examples we can source, and treat any from-price on the linked listings as a dated starting point.
How does the North Flag compare with the Black Bay and Ranger?
The North Flag is the most technical-looking of the three and the only one with a power reserve window. The table sets the practical differences side by side.
| North Flag | Black Bay | Ranger | |
|---|---|---|---|
| Style | Utilitarian, skeletal numerals, power reserve window | Vintage diver, rotating bezel | Field and explorer watch, fixed bezel |
| Bezel | Fixed | Rotating | Fixed |
| Date | Yes, at 3 o'clock | Varies by model | No; current Rangers (36 mm 79930 and 39 mm 79950) are time-only |
| Distinctive feature | Power reserve indicator | Snowflake hands, dive heritage | Expedition heritage, simple dial |
Choose the Tudor Black Bay if you want a rotating bezel and the broadest range of sizes and colours. Choose the Tudor Ranger if you want a cleaner field-watch dial with a current-production movement. Choose the North Flag for the power reserve complication and a design that looks like nothing else in the range. If water resistance beyond 100 m is the priority, the Tudor Pelagos is the dive-rated option, and our Pelagos guide explains the differences. The wider line-up, including the dress-leaning Tudor Royal, sits in the Tudor collection.
Is the North Flag still in production?
Reports indicate that Tudor has discontinued the North Flag, so it now trades mainly as a pre-owned or leftover new-old-stock watch. That has two consequences for buyers. Availability is thin, which is why a sourced search works better than waiting for a listing, and condition matters more than usual: ask for the guarantee card, the extra strap or bracelet if it came with one, and clear photographs of the dial and case. Because the watch is no longer a headline model, secondary-market asks have generally sat below those of comparable sports models, though they move with supply.
Who is the Tudor North Flag for?
The North Flag suits a buyer who wants a robust everyday steel watch with a real mechanical talking point and does not need a dive bezel. It wears at 40 mm on most wrists, the brushed finish hides daily scratches, and the 70-hour reserve is useful if you rotate watches. It is less suited to someone who wants a diver, a very clean dial or a model that is easy to find new. For a first Tudor with a distinctive personality, it is a strong candidate; for a first Tudor that will be easy to resell, the Black Bay is the safer choice.
Quick answers
What movement is in the Tudor North Flag?
The MT5621, Tudor's first movement made entirely in house. It is automatic, COSC certified and has a silicon balance spring and about 70 hours of power reserve.
How long is the North Flag power reserve?
About 70 hours, which means it keeps running through a weekend off the wrist. The indicator at 9 o'clock shows the remaining reserve.
How big is the Tudor North Flag?
The M91210N has a 40 mm stainless steel case with 100 m water resistance and no rotating bezel.
Is the Tudor North Flag discontinued?
Reports say yes. Confirm with an authorised retailer, and expect pre-owned or leftover examples rather than steady new supply.
Is the North Flag a good watch?
Yes, for the right buyer: a well-built in-house chronometer with a long reserve and a distinctive dial. It is less of a mainstream pick than the Black Bay.
Get your Tudor North Flag sourced
Tell us the model, size, dial and bracelet preference, whether you want new or pre-owned, and your budget and timing, through our sourcing enquiry form. We confirm the specific watch, photographs and final price before you commit. Reserve the search with a $200 deposit, credited in full to the price of the watch.
Related reading: Tudor Black Bay 58 guide · Tudor Pelagos guide
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