The post on the German forum I found it on claimed it was a one-man tank, but gave no further details.
Clearly as it has two head covers, it is at least a Two Man tank.
Still, I've never seen it before. Only 4 road wheels? Bizarre. The head covers date it to Christies later experiment years though. It could be that it never made it into the Tank books because it was in fact an armored car - but the traditional double road wheels seem to show it was indeed a wheel & track vehicle.
There's another photo of this in "Encyclopedia of Armoured Cars" by Duncan Crow and Robert J Icks (1976), page 126. It is described as a Christie commercial armoured car from 1933. It was 4 x 4 and the book confirms two crew (or at least, two crew cupolas). No mention of this being a wheel and track vehicle, and I don't think it was. The book also gives dimensions, but they don't look right.
I was suspicious about it being a tank to start with, due to the widely spaced apart wheels (which, as Vilkata points out, are identical to those on some Christie tanks). However, the M1919 has very widely spaced apart roadwheels... http://mailer.fsu.edu/~akirk/tanks/UnitedStates/mediumtanks/usmt-ChristieM1919.jpg ...albeit with a sprung wheel unit in between.
The strange 'axle' that protrudes from the front of the machine in Vilkata's picture looks like it may carry idler wheels for tracks, a la this (see lower picture)... http://www.sg.hu/kep/2004_12/sg2_1.jpg ...though in the linked image they appear to be on sprung arms.
Vilkata's strange machine seems to have features of both tracked and untracked vehicles, but without alteration looks unsuitable for tracks. Therefore, perhaps it is an armoured car, but one adapted from a tracked chassis?
The similiarity with Christie's commercial tank designs of the period is unmistakeable, but I think the distance between the wheels and no sign of any missing wheel between make this a very unlikely tank or wheel-cum-track machine. Besides which, the authors of "Encyclopedia of Armoured Cars" would have been about at the time (well, Robert J Icks was anyway, Duncan Crow would have been in the UK). I wouldn't be surprised if Icks knew Christie. So I'm prepared to believe them when they say it's an armoured car.
I don't doubt that it's an armoured car, but I do wonder if it was adapted or converted from a tracked vehicle, perhaps a tracked prototype that failed.
My point was that there are elements in common with some Christie tracked vehicles that seem redundant on a machine if it was designed from the off as a wheeled vehicle. For example, the odd sloped 'shelf' with axles at the front of the armoured car is very similar to the front of this 1931 Christie tank: http://mailer.fsu.edu/~akirk/tanks/UnitedStates/mediumtanks/usmt-ChristieM1931.jpg
That's a fair point. It might well be a failed tracked vehicle converted.
I suppose it could be the "shelf" was intended to mount two small wheels to help it climb slopes? It is undeniably a very odd design whether it started life as a tank or an armoured car.