Photos: A century of helicopters

The Sikorsky S-64 Skycrane design, which dates back to the early 1960s, did away with all but the basic elements of a helicopter airframe so that a larger portion of the engine's power could go to lifting an external load. This flying-crane design is no longer in use by the military, which preferred to also have a cabin in the aircraft, but can still be found in commercial and other civilian operations such as transporting lumber or (with a water tank attached) fighting fires. S-64s can lift in excess of 20,000 pounds.

In the early 1990s, Erickson Air-Crane took over as the manufacturer of S-64s. Erickson's Helitankers carry a 2,650-gallon tank system and can spread both water and fire retardant.