Armor: December 18, 2003


: The M1 Abrams is the first and (with a few exceptions) only gas turbine powered main battle tank. Similar to a helicopter gas turbine, its AGT-1500 engine is very compact and has a tremendous power to weight ratio, making the Abrams the fastest accelerating tank in the field today. Unfortunately, the Abrams' fuel consumption horribly high, about 5 gallons per mile, a number that does not go down much at idle because, unlike a diesel engine, the turbine is still turning even when the tracks are not. 

At the time the tank was conceived, this poor fuel consumption wasn't considered an issue. The Abrams' design was optimized for NATO's Central European Theater with the Army's aggressive Airland Battle Doctrine in mind. This new doctrine called for fast-paced maneuvering. Because German terrain was rough and heavily forested, which limited distance; it fit the Abrams power plant like a glove. The tank's power gave it the required speed (a top speed of 72 kilometers an hour versus the British Challenger's top speed of 59 kilometers an hour) and its poor fuel economy mattered significantly less over short distances. 

It was the 1991 Persian Gulf War that highlighted the limits of the Abrams' specialized design and Army doctrine. Charging through the Iraqi desert west of Kuwait, the Army's VII Corps struggled to keep four armored and mechanized divisions synchronized (tanks and other vehicles moving together) for a simultaneous attack on the Iraqi Republican Guard. Synchronization meant frequent stops and slow downs to keep a common pace among thousands of vehicles. The Corps could only move as fast as the slowest element if it was to stay together. Most telling, when units halted to refuel, the Abrams' tanks were empty while other vehicles, including tracked Bradley Fighting Vehicles, had quarter- and even half-filled fuel tanks. The pace of the battle was slowed in a way the corps commander didn't believe he could change. The Abrams drank too much gas and Army doctrine said that synchronization was vital. He couldn't abandon the Abrams and he felt desynchronizing his force would result in friendly fire. The "slow" pace of VII Corps is blamed by some for the escape of Republican Guard elements in the last days of the war.

After the war, a Defense Science Board report highlighted the Abrams gas-guzzling as a problem and the Army sought a number of technical solutions, including JP-8 fuel, an improved fuel control system, Auxiliary Power Units to allow the turbine to be shut off more often, and a replacement engine. The simplest non-technical solution was the new operational approach used in Operation Iraqi Freedom in 2003. 

Because the Abrams burns almost as much fuel at idle as it does on the move, the 3rd Infantry Division simply did not stop moving from the Kuwait-Iraq border to the outskirts of Baghdad. The latest iteration of Army doctrine, FM 3-0 Operations, still lists synchronization as a tenet of Army operations, but this time the emphasis was put on other tenets: initiative, agility, and depth. Synchronization went out the window, allowing one brigade of the 3rd Infantry Division to speed 240 km in 40 hours versus VII Corps' Desert Storm attack of 160 km in four days. The Abrams was still a gas hog, but the fuel was burned moving instead of standing still. 

To replace the Abrams' tired AGT-1500 engines, the Army planned to develop a new gas turbine, the LV100, for the Crusader howitzer and a future M1 upgrade. With twenty years of technology to build on, the LV100 was to have improvements such as hotter core temperatures for better fuel efficiency and fewer bolts to reduce rotor stress and increase length between inspections and replacement. Unfortunately, fewer than a dozen LV100 prototypes were built before the Crusader program was cancelled, taking the LV100 with it. Testing of these engines was not completed but the program expected to reduce the number of parts in the engine by 43 percent versus the AGT-1500 and improve the efficiency by 30 percent. The cancellation leaves the Abrams to soldier on with the aging inefficient engine and growing maintenance problems.

The US Army of the late 1970s and 1980s had a laser-beam focus on war in Central Europe. The Abrams might have done well there. The deficiencies we see today lie at the crossroads of technology, doctrine, and strategy and will not be easily corrected. Where and how will the next war be fought? The better we are able to predict these issues and the better design tradeoffs we make, the more effective our next generation weapons will be. --AJ Wagner




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