In similar fashion, steam engineers knew that fire-tube boilers were archaic in comparison with the modern water-tube variety so well-proven in marine and stationary service. Batches of locos with water-tube boilers were built, but proved expensive to maintain in the face of roadbed hammering. Fire-tube boilers were no picnic, but they were maintainable; when a loco came in from a run, its fire was dropped, planks were thrown onto the fire grate, and a man in heavy protective gear clambered into the firebox, where he used a soapstone crayon to mark leaking fire tubes (leaks were easy to see – each one was jetting steam at 380F). Later, other men would caulk those leaks with pneumatic hammers. A fresh fire was set and the machine went out on the road again.