In the mid 1960's there was a shortage of wagons even though there were about 24,000 freight vehicles in service, most of them four wheelers.
More wagons were required for superphosphate traffic. As open wagons were in short supply it was decided to use _M__ cattle trucks.
About seventy vans were modified by lining the interior with tarpaulins. The wagons were then loaded with bagged superphosphate by hand. The modified wagons were reclassed to MS.
By 1970 the MS trucks were scrapped or had been returned to normal cattle traffic.