Tracked motorcycles are a continuous source of fascination and back in the early 20th century, numerous prototypes were being built, usually with military applications in mind. This one is new to me, it's a 1937 Mercier, 1 of 3 prototypes built for the French military.
The obvious difference between this example and the others most of us have seen is the front track / front drive arrangement. A JAP (J.A. Prestwich) 350cc engine is used for power running through a 3 speed transmission.
This example, located in France, is currently for sale on eBay and there is no other information given with the listing though they say it works perfectly and from the looks of it, it was either kept in some museum or restored to its current condition.
Tracks on a motorcycle seem perilously close to a solution looking for a problem. Most any anticipated situation where something like this might be used, an off road motorcycle would probably work as well or better, certainly today, though perhaps not back in 1937, given the capabilities of an off road bike of the time. But back then, the spirit of invention was running full speed and all sorts of ideas were being tried. I think it's neat.
More photos and link below:
UPDATE: Walt's comment below and my response made me do a little digging and here is the cover of Popular Science that I was referring to.
Link: Auction has ended