I don't remember what year it was, or what occasion brought Dad and I to visit Grandma that summer evening, but I remember that big white Mercury in Grandma's driveway as clearly as I remember anything, even though I couldn't tell you if it was a Montclair or a Monterey or a Monty Python, or which one of my many aunts and uncles owned it. I remember it so clearly because it it had the coolest back window I'd ever seen.
You see, the back window could be rolled down.
For most of the brand's existence, the average Mercury has been a badge-engineered Ford, usually with a slightly nicer level of trim and a slightly softer suspension and a slightly higher sticker price. However, for a period of several years beginning in the late 1950s, some full-sized Mercurys had a distinct roofline. The trailing edge of the C-pillar (the one behind the seats) was "reverse slanted" so that the bottom was further forward than the edge of the roof.
This wasn't the only use of a reverse slant C-pillar: Studebaker's "Loewy coupes" of 1953-55 had this styling cue, as did the Packard "Balboa X" and "Predictor" show cars, and AMC's 1956 Rambler notchbacks. On the Stude, the rear window was conventionally sloped and wrapped around into the C-pillars. On the Packard show cars and the Ramblers, there was instead a more or less flat piece of glass across the back mounted flush with the rear edge of the pillar.
Ford first used a similar roofline on the D-524 show car of 1954, with the rear glass flush with the back of the C-pillar, like the Packard and AMC. The D-524's rear window rolled down for added cabin ventilation--a feature also found on the Packard show cars, but not on the Ramblers. This rear window treatment appeared on a few more styling studies and show cars before making its production debut on the 1957 Turnpike Cruiser, where it was dubbed the "Breezeway." Other cars in the '57 Mercury lineup got the reverse-slant C-pillar without the roll-down window, and Lincolns and some Edsels had a similar C-pillar with a wraparound backlight.
The Breezeway roof gave the full-sized Mercurys a distinctive look, disguising the fact that they shared much of their sheetmetal with their Ford (and Edsel) stablemates. More importantly from the customer's standpoint, you could roll down the rear window and open up the cowl vent and have a nice flow of fresh air through the passenger compartment at cruising speed without rolling down the side windows. It was quieter than running with the side windows open, and the rear seat passengers would stay dry even in a light rain! This was an awfully nice feature to have on a muggy "dog day" in summer--especially back then, when air conditioning was an extra-cost option of questionable reliability that sucked power from the engine like one of Twilight's vampires whenever you flipped it on.
The overdecorated Turnpike Cruiser was a bit of a flop thanks to the 1957-58 recession, but the Breezeway rear window was revived for Mercury's 1963 model year, and offered through 1966. (It also appeared on some '58 and '59 Lincolns.) After it was discontinued, Mercury continued to offer a retractable rear window in a modified "fastback" form through 1968.
Though clever and distinctive, the Breezeway rear window wasn't really all that popular as a selling point, and the development of flow through cabin ventilation and better A/C eventually canceled out its advantage in passenger comfort. In today's world, where a main objective of body design is to reduce drag, a drag-inducing "back-slash" rear window would probably never even be considered.
It sure was cool when they rolled it down, though.
--Cookie the Dog's Owner
The advertising images from the 1964 Mercury catalog were uploaded to Flickr by user "paul.malon." The photo of the '64 sedan comes from How Stuff Works. For a more complete telling of the Breezeway story, I recommend this article at Ate Up With Motor.