You're right; that was the answer -- the drive sprocket is the giveaway. It's a Grizzly, the variant of the Sherman produced in Canada. The Montreal Locomotive Works built 188 of these tanks from September to December 1943, but production was stopped when it became apparent that the US plants manufacturing Shermans had more than enough capacity to provide for all users. It differed from the standard M4A1 only in details -- it used CDP (Canadian Dry Pin) tracks, which were stronger than the standard Sherman tracks, it had a British 2" smoke mortar in the turret roof, and a No. 19 radio in the turret bustle.
"After the decision was made to terminate Grizzly production in 1943 in favour of US-built types, the Canadian vehicles were issued to train future tank crews in places like Camps Borden in Ontario, and Utopia in New Brunswick (later CFB Gagetown). According to recent research out of the UK, it does not appear that any Grizzlies made it to Europe by the end of hostilities: however one Royal Armoured Corps liaison letter states that "A limited number is being obtained and will begin to be issued to 21st Army Group in approximately mid-July 1945". When taking into account the shortage of Shermans in the last months of the war, as Peter Brown points out, it seems odd that they would suddenly have "discovered" the existence of these vehicles and had them shipped to the UK. One possibility is that the Grizzlies remained in Canada for training purposes, therefore negating any further demand for Shermans in Canada, and perhaps obtaining the Grizzlies from Canada was seen as somewhat of a last resort.
"Whatever the reasons for this, the Grizzlies remained in Canada for training until the late 1940's and early 1950's, when a significant number were sent to Portugal to help equip their tank force. They remained in use until the 1970's when a number of Grizzlies, Sextons and even a few Stuarts were disposed of through private sources. One collector/importer acquired as many as 40 Grizzlies and 7 Sextons in the early 1980's, with some examples going for as little as 7500 Pounds each. Most of the vehicles were in running condition and had had their main gun barrels cut off a few inches in front of the gunshield, but the barrels had been thrown in the hulls so collectors could reattach them for cosmetic purposes. Photos show most, if not all the Grizzlies retrieved from Portugal had CDP track and a surprising number had the US type all-round commander's vision cupola, while others had the more common split hatch. Grizzlies are now a very common sight at European rallies, and one can be seen (the CDP drive sprocket at least!) -very briefly- masquerading as an M4A1 Sherman in the last few frames of the film "Saving Private Ryan".
"It is perhaps a little unusual that so many Grizzlies survive to this day when only 188 were made, with many in the hands of European collectors and several in Canadian museums. In the mid-1990's several more were found in a scrap yard in Portugal, including one possible Skink hull, and were cut up for scrap. Canadian authorities apparently were not interested in obtaining any, although a few may have found their way into the hands of collectors in the US and Europe."
