These models of a military half track truck and field gun are built from "Meccano Army Multikits". These sets were introduced in 1973  in what was a radical departure from the then current range of traditional sets. These new sets enabled a range of themed models to be built with special parts, there were two new sets Army Multikits and Highway Multikits. All the parts of the army set were finished in semi matt olive green, the small parts, nuts and bolts were anodised black. Included was a ready made steel cab in two parts and four large chunky plastic wheels, somewhat different to the thin plastic road wheels that came with sets at that time. These sets were made up from existing standard parts except for the plastic gun barrel. All the standard parts were re-numbered to distinguish the Army parts from standard parts although they were not available to purchase as extras. The set also included flexible caterpillar track, this had been introduced as an accessory pack into the Meccano system in 1971.The set manual was a very lavish, glossy full colour brochure, illustrating in step by step photographs the construction sequence for each of the ten different models, shown on the cover illustrated at the bottom of this page. The sets  marked another change in the Meccano system, the introduction of hexagonal nuts replacing the traditional square nuts. This was not the first military style set made by Meccano, in August 1939 on the eve of the Second World War the "Mechanised Army Outfit" was luanched, a very similar concept to the Army Multikit of 33 years later. One of the models that was shown in the instructions was a Half Track Truck. The 1939 set had a useful feature not included in 1973, the gun barrel sections were transversely bored to enable them to be pivoted.  In the 1973 Multikits the gun barrels have to be clamped between parts.The sets remained in production until the closure of the Binns Road, Meccano factory in 1979. Many sets were around for many years later, unsold, as were parts. In autumn 2020 I was given two Army Multikits not something I have ever been interested in but the owner said, if I did not take them they were going to re-cycling so I took pity on the sets! One was hardly used and still had the full set of stickers, the other set was in play worn condition. In an idol moment I thought I would see what could be constructed, I choose from the manual a Half Track Truck and a Field Gun using the parts from both sets. I followed the instructions with a few changes the main one was to improve the tracks by lengthening them and adding additional 1" pulleys with rubber rings. The field gun was more or less as the manual with exception of not making the gun fire plastic shells with a tension spring. Mechanised Army images courtesy of Malcolm Hanson Page published May 18 2021 Revised 29/06/2021
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HALF TRACK TRUCK FROM THE 1939 MECHANISED ARMY OUTFIT MANUAL