The Tank Must in steel is the no-nonsense entry point into the Tank family: manual-wind, in-house movement, 31mm, and none of the fuss that comes with gold or lacquered dials. Cartier relaunched the Must line in 2020 with calibers built in La Chaux-de-Fonds rather than bought in, which changes the ownership proposition entirely. If you want a Tank that wears as a daily tool watch, this is the one.
What it is
The Tank Must name goes back to the 1970s, when Cartier created a more accessible Tank tier aimed at younger buyers who wanted the silhouette without the precious-metal price. That original Must line ran on ETA-based quartz movements and gold-plated cases, deliberately positioned below the yellow-gold Tank LC. Cartier discontinued the Must in the 1990s as tastes shifted, but brought it back in 2020 with a meaningful upgrade: the 1917 MC manual-wind caliber, designed and made in-house.
The 2020 relaunch also separated the Must into size variants, with the 31mm sitting between the smaller 25.5mm and the larger 34mm. Steel was added to the lineup alongside gold and gold-on-steel options, giving collectors a version that can be worn without hesitation every day of the week.
Buying notes
The 31mm case reads smaller on the wrist than most modern dress watch buyers expect, particularly on larger wrists where the lug-to-lug span can look compressed. Make sure you have handled one in person before buying remotely. The manual-wind caliber requires daily winding, which some buyers discover they dislike only after ownership.
Straps on the Tank Must use a proprietary Cartier deployment buckle and integrated strap sizing; aftermarket strap options exist but fitting requires attention to lug width and deployment buckle compatibility. On the secondary market, watch for replaced crowns, as the winding crown on the 1917 MC is a high-wear point and a non-Cartier replacement changes both the look and the resale value. Finally, box and papers significantly affect resale on entry-tier Cartier pieces; a Must without full documentation trades at a meaningful discount.
Market read
New retail for the steel Tank Must 31mm sits around $3,800 to $4,200 depending on dial color and retailer. The secondary market hovers near or slightly above retail for complete examples, reflecting healthy but not speculative demand. The steel variant trades more quietly than the gold versions, which means patient buyers can find fair deals rather than fighting auction competition.
This is not a watch that appreciates aggressively, but it holds value steadily because the demand is driven by actual wearers, not flippers.
Service expectations
The caliber 1917 MC is a Cartier-manufacture manual-wind movement serviced exclusively through Cartier boutiques and authorized service centers. Cartier recommends a service interval of roughly four to five years under normal use. Independent watchmakers familiar with Cartier movements can handle the work, though Cartier OEM parts are only available through authorized channels.
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