[Hanno Spoelstra]

About the Canadian involvement in the development of the Mk.3 carriage (source: http://www.forces.gc.ca/dhh/downloads/ahq/ahq073.pdf):

25-pr Carriage for Upper Register Firing

24. It became increasingly apparent during the Italian campaign that some modification to the 25-pr gun was desirable to enable the gun to be fired at elevations greater than those for which it was originally designed. "Upper Register" implies angles of elevation greater than 45 degrees. The method of achieving these high elevations in the field with existing equipment was to "dig in" the trail, that is to say dig a pit behind the gun so that by lowering the trail below ground level the elevation of the barrel was correspondingly raised. Obviously this digging in consumed time and delayed the deployment of guns when "upper register" was required.

25. To meet the requirement an officer of the Technical Liaison Group at C.M.H.Q. designed a hinged trail for the gun which, it was anticipated would allow an extra 15 degrees of elevation. A prototype of the design was made by No. 2 Canadian Base Workshop, England, in May 1944 (53). Trials were carried out during the summer. While these trials on the whole were satisfactory, it appeared that trouble might be expected in service due to the difficulty in excluding dirt from the hinge. Consequently, the Chief Engineer Armament Design (C.E.A.D., Ministry of Supply, U.K.) was asked to redesign this modification, incorporating improvements to exclude dirt (54). The Ordnance Board expressed the opinion that "the use of upper register firing is insufficient to justify the modification of the equipment", but considered "that this modification should be borne in mind for possible inclusion in new designs of equipment: (55).

26. The redesigned prototype (Carriage, 25-pr, Mk 3) was ready for trials in January 1945. As a result of the trials the Ordnance Board recommended the approval of the design (56), and it was adopted shortly thereafter for use on all future production of short axle 25-pr carriages (57). The finalization of the design came too late for production equipment to see service.