Gentle yellow giants: prowl the Arctic: CATCOs: truly a cat for all seasons.

• Author: Martin, Gary L.

CATCOs might be described as gentle yellow giants; with eight big, soft paws that love the environment, they might also be de scribed as the ultimate all-terrain vehicles or rollagons.

Crowley Co. owns nearly two dozen of these vehicles; they are used as a total support system for drilling operations on the North Slope. CATCOs are employed to transport extremely heavy equipment, materials, water and personnel. They are also used as drilling-rig supports, and their all-terrain capability allows the vehicle to be used in the pioneering stage of constructing ice roads.

CATCOs come in two versions (RD 85 and RD 105); they are identical except that the RD 105 has a fifth set of tires installed under its cargo dock. That difference raises the vehicle's payload capability by 15,000 pounds, to 45,000 pounds.

Dubbed land barges because of their uncommonly large carrying capacities, CATCOs have been around for several decades. Crowley Co. obtained them to fill the need for an effective transport machine that is functional in most climates and environments while remaining environmentally friendly. Over the years, there have been many upgrades and modifications to the machines that have improved their overall function and performance.

They operate on ice and snow fields, delicate tundra, sod, swamps and marshes, and on desert sands. This is particularly valuable for pipeline operations on the North Slope, where the weather and terrain can be extreme and the ecosystem fragile.

Part of the vehicle's success is attributed to its large specialized tires. They are often described as 54-by-68inch airbags; they do not have treads and each tire is top-roller driven and can form to virtually any terrain.

Air pressure for each tire can be in dependently controlled, and it is possible to do that while on the move by the vehicle's single operator. The payload is distributed over a very large ground area, at an extremely low pressure-about 4 pounds per square inch. The ground pressure is so light that Crowley has a video that shows a 26,000-pound CATCO successfully rolling over a young woman lying in the sand.

Drive rollers, over each tire, places the vehicle's weight and the weight of its load directly on top of the bag producing friction and torque. This not only increases traction, it also results in the payload riding, in essence, on a cushion of air.

Each vehicle is powered by a Caterpillar diesel engine with 280 horse power. Steering the yellow giant is done...