In 1917 Louis Cartier looked at the Renault tanks on the Western Front and drew a watch. Harper's Bazaar describes the result well: the rectangular case echoes the top view of the vehicle, the brancards, the vertical sides, evoke the treads, and the case itself stands in for the cockpit. A war machine turned into a wristwatch, and it still looks like nothing else.

The Cartier Tank Solo is the plain-spoken version of that idea. It launched in 2004, and the formula is short: a steel case, blue hands, a Roman dial and a sapphire cabochon on the crown. Cartier replaced it with the Tank Must in 2021, so every Solo you can find now is pre-owned. That is the main thing to know before you shop, and I would treat it as a plus: you are choosing from a finished run, not a catalog.

Here is where I would begin, in steel. The XL WSTA0029 and the XL W5200027 share a 31 x 40.85mm automatic case, with a date window on the first, and either one reads as a real watch on a slim wrist. The XL W5200028 comes on a steel bracelet, which dresses it down nicely with a gray knit and straight jeans in October. For a quieter wrist I would go small: the W5200005 on grained black leather, or the white-dial W1018355. The pink dial on the mid size Ref 3170 is the fun one, and I can see it with a camel coat.

Because these are pre-owned, the check is simple. Look at the corners of the case for rounding from old polishing, make sure the crown cabochon is clean, and ask whether the strap is genuine Cartier. Papers are a bonus, not a given.

Not every Tank Solo is steel. Cartier made the same shape in 18k yellow gold, rose gold and the steel-and-gold mixes, and the only way to tell them apart quickly is to look at the case back and strap. The small W5200002 in yellow gold has a steel back and a dark brown strap, and it is the one I would pair with a cream turtleneck and a camel skirt.

The W1018755 is the same idea on black leather, a little sharper, better with a black blazer. The two W5200004 watches are the large size, 27 x 35mm, in yellow gold and steel, one on brown and one on black Cartier leather. If you wear gold hoops, this is the middle road: it reads warm without going full jeweler's window.

Rose gold is where I would look if your skin runs pink or olive. The W5200025 and W5200024 are quartz on leather, and the W5200026 is the XL, in two versions: one with a silver dial and date, one with an ivory dial and blue steel hands. The ivory one is the softest of the bunch, and I would wear it with an oatmeal sweater and wide trousers.

Buying test: gold-and-steel watches show wear at the steel back, so ask for a photo of it. Check that the gold sides have no deep scratches, and that the crown turns cleanly.

What I would skip: a gold Solo on a strap that has clearly been replaced with a non-Cartier one. The strap is half the look.

Cartier brought the Tank Must back in 2021, and GQ's report from that year was clear that it replaces the outgoing Tank Solo. The name is older than that. The first Must de Cartier arrived in 1977 as a quartz-era alternative, with gold plating over a silver base instead of solid gold. So this section has two eras on purpose.

The modern ones first. The WSTA0040 is the XL, 31mm and automatic, with its original box. The WSTA0052 is large steel with a sapphire cabochon crown, and the WSTA0041 on leather is the one I would wear with a trench and loafers this month. The WSTA0051 and the petite WSTA0060 are the small ones, both steel with silvered Roman dials, and both sit nicely under a cuff.

Then the vintage Must de Cartier pieces, in vermeil, which is gold-plated sterling silver. The 1980s small model with a pale lemon dial is a quiet little thing, and the LM 590005 with a black dial is sharper. The Ref 2415 in purple, a Japan limited edition of 500 from around 2001, is the odd one out and I like it for that.

Buying test: with the vintage plated ones, the gold can wear through at the corners of the case, so look at the edges in close photos. For the modern steel ones, ask whether the original papers are included. The WSTA0041 and WSTA0051 list them.

What I would skip: a plated Must if you plan to wear it every day in the shower and at the gym. It will tell on you.

The Tank Francaise came in 1996, and the story goes that it went back to a squarer case and added a link bracelet, inspired by the original Normale. That bracelet is the whole point. It turns a dress watch into something you can wear with a T-shirt.

The Francaise watches here is all steel on the integrated bracelet. The W51002Q3 is automatic with a silver dial, the W51011Q3 is a 25mm quartz with the blue cabochon, and the WSTA0074 is the medium model from 2023. The W51028Q3 has a pink mother-of-pearl dial and black Roman numerals, and if you wear a lot of gray and navy, that is the small detail I would go for.

The Americaine is the stretched, curved one. The large WSTA0018 and the WSTA0045 are 45.1 x 26.6mm automatic cases that bend around the wrist, and they are bolder than any Solo. The mini WSTA0116 in steel and the mini WGTA0341 in rose gold are only 28mm long, with sunray dials, and they look best with a stack of thin bangles.

Fitting test: the Americaine is long, so check the length against your wrist bone before you commit. The mini will sit comfortably on a narrow wrist, the large will not. On the Francaise, ask about the links: bracelets that have been resized sometimes lose the pieces.

What I would skip: the large Americaine if you mostly wear a fitted sleeve. It will catch on every cuff.

The Tank Louis Cartier is the one that set the standard. It was born in the early 1920s as a modified Tank Normale, with rounded brancards, and Tank Louis is still the shape most people have in their head. Warhol famously said that he did not wear a Tank to tell the time, and I think that sums up the whole appeal.

In yellow gold, the W1512856 has a white Roman dial on leather, and the mini WGTA0352 has a grained silvered dial and is only 24 x 16.5mm. The WGTA0343 is the medium at 33.7 x 25.5mm, with blued sword hands, and it is the one I would wear with a white shirt and gold hoops. The WGTA0092 in rose gold is large, manual wind, with a gray dial and a beaded crown, and it is the most unusual of them.

Then the vintage ones. The 1970s Tank Louis 78086 is 23mm and manual wind. The two Tank Normale 78093 watches are smaller still, at 20mm and 18mm, with one quartz, and they are the ones for people who want a barely there watch. The 1940s Tank with the original gold brick bracelet is the collector's pick, and it is the one to study before you buy.

Buying test: with the older gold pieces, ask when it was last serviced, and whether the movement is original. Check the crown, the dial for spots, and the engraving on the case back.

What I would skip: a vintage Tank in poor condition just because the reference is rare.

I would begin with the Solo, since that is what the edit is about: steel first, because it is the shape in its simplest form, then gold if you want it warmer. Pick the size by your wrist, not by the look in photos, and only then think about dial color.

If the Solo is not your watch, move to the Tank Must or the Francaise for a bracelet. Keep the Louis for a slow day, and the vintage ones for when you are sure.

Louis Cartier saw a tank from above in 1917 and made a rectangle. More than a century later, I still think that is the neatest idea in watches. If you want to keep browsing, I also put together Cartier Tank Watch Dupe and The Cartier Watch for Women.