Packard was known for its masterful V12 engines, but an inline 12? That’s an entirely different animal, one worthy of a closer look.

Among all the weird and wonderful piston engine configurations tried over the years, the straight 12 isn’t totally unknown. To name a few, Frank and August Duesenberg built a pair of inline 12 engines in 1913 for Commodore James A. Pugh’s marine racer, Disturber IV. Automobiles Corona of Paris briefly advertised an inline 12 in 1920, and the always eccentric Gabriel Voisin sampled the layout as well, although his V12L was more like a pair of sixes joined at the crankshafts. Today,  Wärtsilä-Sulzer offers its mammoth marine diesel engines, which boast 100,000 hp and more, in an inline-12 version.

But in a production automobile, an inline 12 is a sketchy proposition. The crankshaft, which must be roughly twice as long as its V12 counterpart, wants to wind and unwind like a big rubber band, producing tremendous torsional vibrations, and bow and whip in the middle like a jump rope. To counter these forces, the crank must be extremely stiff and heavy, while the cylinder block must be extremely robust as well to contain all these unwanted motions, and also to withstand all the twisting and bending forces of the chassis. It’s not the most attractive or efficient package, to say the least.

But none of that deterred the Packard Motor Car Company in 1929, which at the time  was among the leading engine manufacturers in the world on land, sea, and air. With the Packard Twin Six of 1914 and the Single Eight of 1924, the car maker had conquered the V12 and straight-eight designs, so from that angle maybe a straight 12 did not seem so preposterous. Or maybe the Packard engineers were simply curious to see if the layout was not quite as horrible as it appeared on paper. Whatever the reason, the company constructed a single prototype.

There’s not a lot of hard information around but in Packard lore, the inline 12 featured a bore and stroke of 3.50 by 5.00 inches, yielding around 577 cubic inches, and presumably it produced in the neighborhood of 150 hp. In most ways, the 12 could be described as an extended version of the company’s successful straight eights, with L-head valve gear and other conventions of the day.

The development program was soon suspended, reportedly due to vibration issues (no surprise there) but a prototype engine was installed in a production Packard chassis with a Victoria body by Dietrich. To accommodate the stupendous length of the engine, the cabin was pushed back around 12 inches on the 145-inch wheelbase and the hood and cowl were lengthened a similar amount, producing the unusual proportions we see in these photos. In the car biz the dimension is called dash-to-axle, and this Packard has some.

In the spring of 1929, the prototype vehicle was handed over to Warren Packard, nephew of company founder James Ward Packard and son of co-founder William Doud Packard. With its flashy orange and silver paint job, the coupe was known around the Motor City as the “easter egg.” Tragically, the 37 year-old Packard scion was killed in a seaplane accident on the Detroit River on August 26 of that year. The car was then returned to the East Grand Boulevard plant, where the engine was removed and reportedly destroyed. Some say the car was then shipped off to a buyer in Mexico, but its whereabouts today are unknown. Packard would introduce a great new 12-cylinder automobile in 1932, but it was of familiar V12 design.