MIL-B-18897F, MILITARY SPECIFICATION: BOILERS, STEAM AND HOT WATER, WATERTUBE (STRAIGHT BARE AND FINNED TUBE), CAST IRON AND FIREBOX, PACKAGED TYPE (40,000 TO 35,000 BTU/HR THERMAL OUTPUT CAPACITY) (06 SEP 1990) [NO S/S DOCUMENT]., This specification covers watertube (straight bare and finned tube), cast iron, and firebox packaged steam boilers and hot water generators.