The Abrams tank.

The_Chieftain:   The turboshaft oil figure you refer to is definitely wrong, I'll say that as an Abrams tanker. We always carried a couple of tins for top-ups, but what tanker wouldn't? The 1,700F exhaust also makes a great coffee cooker, sleeping-bag dryer, and infantry-warmer. The heat signature isn't so much of a problem: It's at the back of the tank, we try not to drive into battle backwards. I've never started a fire with my exhaust, and we train in some pretty dry grass and scrub in California.  

The_Chieftain:   Yes, fuel consumption is generally higher. We don't care. We in the US military have enough tanker trucks and fuel to do the job. I don't believe we've ever had to call off an attack because the tanks ran out of gas, and the reason is that it actually sucks a lot less fuel than people think. For the record, at Tactical Idle, the Abrams sucks 17.5 gal/hour. That's still a good 28 hours of idling on a full tank of gas, not that any tanker would do that. (Full idle consumes less, but I don't know what the figure is, but Wiki says 10/hour. There are 503 USG in the fuel tanks, so 50 hours).    The story of the auxilliary power unit is a sad one. Carnage is correct that the original APU mounted on the left rear of the hull was a bit of a disaster, and removed. The next program was the UAAPU (Under Armor Auxilliary Power Unit), which was a tiny little turbine. It replaced a 55gal cell, so reduced overall fuel in the tank to 448USG, while drinking a rather unfortunate 8.5USG/hr.  Then they came up with another under-armor, based on a rotary engine. That failed to lack of money. . Finally, an external APU was procured which sits in the turret bustle, it's the current solution and I've not seen a tank without one in years. It consumes 1.5gal/hour or so. So that's about 330 hours of idling, if you have a particular need to do that. Not that you would.   -Ammunition or lack of certain type.  Its anti-tank rounds are legends and I am sure the newer ones are even better, no problem.  But to date there has been no anti-personnel round fielded for it except canister which has no better range than the COAX MG and is dangerous to fire past infantry (note: I said "past" not "over", never fire main gun rounds over friends).  I personally know how important a tank's coax is to its defense and infantry support but HE-FRAG rounds can be just as important, they have much better range and accuracy and cause instant area effect.  They are totally important when engaging anti-tank teams, especially ATGMs which can be farther than the COAX or AA gun's effective range.  Same can be said against urban areas or dug-in positions.  While sabot and HEAT rounds are powerful they will not do nearly as much damage to structures and have very little area effect.  Why an HE-FRAG has not been fielded for Abrams, especially with the nature of conflict in Iraq 2003-2011, is very confusing to me.   It is confusing to me too, since the USMC have been fielding HE rounds for their Abrams tanks for the last few years (DM11 Multi-purpose high explosive). There is no mechanical reason why M1 can't fire HE rounds. It can. The HE-Obstacle Reducing round has been in Army service for some time, though granted, it's designed, as the name implies, for blowing things up, not killing people. Up until now, though, the Army has generally considered that the .50 cal and the accompanying Bradley can deal with the softer targets. This is changing, with the advent of the  XM1147 High Explosive Multi Purpose (AMP) round. In any case, the reason the Abrams has not used HE-Frag in the US Army is because the US Army didn't feel any need to buy or produce the ammunition, not because the tank was incapable of using it. That should not be held against the tank.