After a series of Association of the U.S. Army (AUSA) annual conventions where the main battle tank was conspicuous by its absence, a General Dynamics Land Systems M1 tank is back on the show floor this year, albeit missing two features — its turret and its turbine engine.

The vehicle shown by GD is a turretless propulsion technology demonstrator for a diesel-powered M1, and the manufacturer says that dynamometer tests performed by the Army in August and September showed a 49% improvement in fuel consumption over the turbine-engined vehicle.

The diesel-powered tank is the result of three and a half years of work performed with independent research and development funding by GD and its principal partner, Germany’s MTU — which already supplies high-performance engines for the German Leopard and Israeli Merkava 4 tanks. The engine on display at AUSA is the 1500 hp., V-12 MTU883. Since the M1 was designed in the 1970s, improvements in materials, fuel injection systems, turbocharging and engine management have made it possible to deliver more power within weight and volume limits and to match the speed and acceleration obtainable from a turbine.

The main challenge in developing the demonstrator — GD’s second run at a diesel M1 — was to package the engine and its supporting systems, including aft-mounted radiator modules, with four hydraulically-powered, variable-speed cooling fans in a space designed around the turbine. One deliberate design constraint was to avoid any changes to the hull structure. The cooling system replaces the turbine’s exhaust — reducing the tank’s thermal signature — and the diesel exhaust is located in the upper rear side area of the hull, above the tracks, using complex mufflers to match the turbine’s lower noise signature. Lower fuel burn means that the fuel cells can be made smaller, making more room for the engine.

The demonstrator also is equipped with new Diehl tracks, drive sprockets and rollers, which are intended to increase track life from 1,200 to 5,000 hr., although these have not yet been road-tested.

The U.S. Army has no formal program to re-engine the M1, but no all-new replacement is in sight, so GD argues that a re-engining program will pay for itself in lower direct operating costs and less cost to deliver fuel to the front line.