23 PILE DRIVERS, LOCOMOTIVE CRANES, CRAWLER CRANES, CONCRETE MIXERS, SHOVELS, CONVEYOR CABLEWAYS, TRACTOR CRANES, DIVING OUTFITS EXCEPT THE SUITS, HOSE LINES, AND CABLE LINES THEREOF; LOCOMOTIVES, DIPPER DREDGES, HYDRAULIC DREDGES, AND CLAMSHELL DREDGES, ALL EMPLOYED IN RIVER AND HARBOR IMPROVEMENTS