What is the history of the classification schemes for locos?
Early locomotives in India had a bewildering variety of classification schemes. Regional railways had their own classification schemes too. For more details on this, refer to reference works such as Hugh Hughes’ classic 4-volume work on Indian locomotives. The first BESA standard classes appeared in 1903. The HPS, SPS, HGS, and SGS steam loco classes were quite popular. HP = Heavy Passenger, SP = Standard Passenger, HG = Heavy Goods, SG = Standard Goods. In these, the suffix ‘S’ stands for ‘superheated’. An alternative suffix ‘C’ indicates a conversion to superheating, e.g. SGC. A suffix ‘M’ was sometimes used to mean ‘modified’, for variant designs. However, these classification codes were by no means universally adopted, and various railways had their own schemes. In 1924, when IR decided to classify engines, the initial notation was: • X for broad-gauge • Y for meter-gauge • Z for 2′ 6″ narrow-gauge • Q for 2′ 0″ narrow-gauge The IRS (Indian Railway Standard) classes XA, XB, XC, XD,
