Dieselisation
Dieselisation took place largely because of the tremendous reduction in operating costs it allowed. Steam locomotives require large pools of labour to clean, load, maintain and run. They also require extensive service, coaling and watering facilities. This was their biggest inferior measure as compared to the diesel locomotive in the number of ton-miles or passenger traffic miles either could run. Diesels could and did have a significantly higher initial price per unit-horsepower delivered. However, their far greater range between fueling stops, the absence of water stops, and the much higher unit availability between inspection repair and maintenance stops, were far better than steam. Diesels simply required significantly less time and labour to operate and maintain. Diesel power was also more scalable to power requirements, owing to the control systems that allowed multiple units to be controlled by one operator. "Double header" steam power required a crew for each locomotive. Initially, diesel locomotives were less powerful than the typical steam locomotives. Between the late 1930s and the late 1950s the power available with diesel locomotive engines roughly doubled, although the most powerful steam locomotives ever built still exceeded the power of the most powerful diesel locomotives from the late Twentieth Century.
Rolling stock of the Korean State Railway
Later, around the late 1960s or early 1970s, a system similar to that introduced for electric locomotives was applied to steam and diesel locomotives. Steam locomotives were universally given the type designator 증기 ("Chŭnggi", "steam") and diesel locomotives 내연 ("Naeyŏn", "internal combustion"), along with a three- (for mainline diesels) or four-digit (for shunting diesels and all steam engines) serial number, with diesel locomotives are numbered sequentially within their number series. On steam locomotives, the first of the new four-digit serial number reflects the former type designator (부러 → 1, 미가 → 6, 마더 → 7; the others are unknown, and the 8000 series is applied to steam locomotives of foreign origin supplied as war aid during the Korean War); the second digit reflects the former type-series, directly translating the number, e.g. 미가서 became 6300, 마더하 became 7100. The last two digits are the locomotive's original running number (last three digits, in the case of the Migaha class numbered into the 6000 and 6100 series). The system behind determining which numeral represents which type designator (that is, why Miga became "6", etc.) is unclear, as this numeral has no relation to anything obvious, e.g. number of powered axles, etc.