If we say "largest locomotive", the question is: "largest" by what measure? You could actually use four (or six):

• length (with/without tender),
• weight (with/without tender),
• tractive effort,
• power¹.

The Alleghenys beat the Big Boys in two categories. At 7,500 HP peak/c. 6,600 HP sustained (drawbar), only Pennsylvania's Duplex types (see one in my earlier Fast Steam diary) could match their power (Big Boy: 6,290 HP). At 350 (metric) tons without tender, they were also a bit² heavier – but not by design, and that explains why they missed the spotlight.

For, the first batch was delivered 25 tons overweight. At over 37 (metric) tons axle-weight, they were more than what tracks were certified for – so while C&O got angry with the manufacturer, they kept the numbers confidential...

In service, the H-8 was successful – unlike most other bigger-than-Big-Boys. Hence, I'll keep the suspense³, and will show two more only in the next instalment of a now starting three-part mini-series: the one on failed designs (which again flows over into the third: on crazed designs). Below I will only show two European giants – which have a story too.

The Hungarian Railways (MÁV) class 601

In pre-WWI Hungary, there were a lot of mountains to scale. Designed for such lines just prior to the war, the 601 class was successful. However, after the war, both the country and the locomotive park was cut up. No big mountains remained in rest-Hungary, while the 601's lines in Croatia and Slovakia were soon electrified – left without fitting jobs, the locos were retired early, not one is preserved.

Which is a shame: when built, they were the most powerful (at 1,735 kW/2,330 HP), second strongest (with US standard calculation: 222 kN/49,945 lbs), heaviest with tender (162.5 t/358,250 lbs) and second without (109.4 t/241,185 lbs) in Europe. (More in German here.)

The Belgian Railways #2096 "Franco" prototype

The largest steam locomotive ever built in Europe was one of its kind. What you see on the outside: a cross between a Garratt and a Mallet, its three articulated parts rest on four groups of wheels (driven by four pairs of cylinders). Its inside is even stranger: like Siamese twins, there are two fire-boxes side-by-side at center, separately feeding the two boilers (forward/back), which were a special Italian design. (Douglas Self – who scanned the above photo – has more description, Gunter's has more data on #2096.)

Its European record on power (2,200 kW/3,000 HP) was beaten later, but on tractive effort (US standard calculation: 419 kN/94,220 lbs), weight (248 t/546,750 lbs) and length (31 m/101'8.5"), it remains unsurpassed – the "Franco" was big even by US standards.

This monster from 1932, tough not a failure, remained a demonstration piece. It was eventually cut up and made into two locomotives by the German occupiers during WWII, both parts ended up in Poland after the war – later unfortunately scrapped.

1. 'Tractive effort' just means the pulling force. But as even railway bosses confuse basic physics, let me explain that power is NOT equal to force. It is force times speed.
   For a steam locomotive, starting tractive effort is pretty much a given from its basic dimensions, but as at increasing speed the cylinders use up steam ever faster, its power is limited by how fast steam can be produced. The latter also depends on what kind of coal you fire – so in the end, the figure that was 'counted' for steamers was tractive effort.
   On the other hand, diesels and electrics have a power source of relatively constant power, and can use all their weight to start a train, so the figure that is 'counted' is power. (However, if weight is smaller, extra power won't help on rain-soaked rails – something rail bosses ordering new freight locos in recent years in Europe failed to consider...)↑
2. Really just a bit. Considering the nominal numbers, with tender the last batch of Big Boys was 3/4 tons heavier, without tender the H-8 with c. 2.5 tons. However, values from actual weightings for both types – both slightly lower than nominal – put the Alleghenies ahead by both measures (then ieagain, we don't know the instrument errors...)↑
3. If you are too curious to wait, you can check tables for each category compiled by US railfan Wes Barris.↑

Previous Monday Train Bloggings:

1. (Premiere/ modern Austrian trains & locos)
2. Adventure
3. Fast Steam
4. Heavy Haul
5. Forgotten Colorado
6. The Hardest Job
7. Blowback
8. Highest Speed
9. New England Autumn
10. Trainwreck