sentences:  The type 30 was produced in three versions.Class 30a had four cylinder high pressure engine, while class 30b and 30c were compound engines.18 units were made of the lightest version the 30a (numbered 256-258, 271-282, and 316-318), there were 23 units of the 30b (numbered 346-368), while 4 units were made of the heaviest version, the 30c (numbered 466 to 469).