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[drcampbell]

An entire submarine displaces (has a mass of) 6,000 tons. Not the reactor, which is a small fraction of that.

A typical long-haul freight train (the entire train, not the locomotive alone) is in the neighborhood of 8,000 tons and 8,000 Horsepower. 200 tons is about right for a freight locomotive.

You're probably right that a train would be hard-pressed to climb a 10-degree grade. But they don't ever need to. Outside of the Rockies, trains seldom encounter more than a one per cent (0.6-degree) grade. Even in mountainous areas, anything more than 2 degrees (3.5%) is very unusual.

A train's ability to climb a grade is limited by wheel slip, not horsepower. Locomotives can typically achieve a tractive effort equal to 1/3 of their weight.
Horsepower does, of course, limit the speed at which they can haul a heavy load uphill. At 1 hp/ton, it's only possible to climb a 1% grade at 20 mi/hr or a 2% grade at 10 mi/hr.

Momentum only helps for the first 100 feet. After that, it's sheer muscle.

One factor which does help a long train is that the entire train often isn't on the grade at the same time. For a short hill, such as the approach & departure to/from a bridge, you first have the front half of the train on the grade and the rear half on the level. Then you have the front half going downhill while the rear half's going uphill ...

(Gandy and I must have been banging away simultaneously)