Quite large Garratts were being built from the mid-1920's on, so I'm not sure the "late in the game" argument works. I think the principal US objection was the fear that as water and coal supplies were used up, a Garratt would lose adhesion. Since Garratts were widely used in countries that had considerable experience with tank engines (which have the same problem) railwaymen there understood that if the engine was built with an adequate factor of adhesion when light, it wasn't going to be an issue.
Garratts tended to be used in places where the rails were light and light axle loadings required. Under those conditions, a Garratt could supply plenty of power while still treading lightly on the rails. In the US, heavy axle loadings were the norm and clearances weren't much of an issue, so large conventional engines and large articulated engines could be used.
One of the biggest advantages of a Garratt is the deep firebox, which has no wheels under it. Most articulated engines had the firebox above the rear drivers, even when there was a four wheel trailing truck present. The 2-6-6-4 and 2-6-6-6 articulateds were among the few that had the firebox entirely over the trailing truck. Unless the engine was of extraordinary size, a shallow firebox was less efficient.
I think that last line answers the question for the US. We could build them big, so the relative advantage of a Garratt was lessened. In South Africa, where Garratts competed directly with Mallets on 42" gauge rails, the Garratt won overwhelmingly.
I think Garratts would have been very effective on US narrow gauge lines, but as has been pointed out, US narrow gauge lines were in decline even before the depression, so the money wasn't there even had the interest been.
Michael Allen
Edited 1 time(s). Last edit at 07/02/2007 07:11PM by trainrider47.