| GNR O1 class LNER O1 (later O3) Class | |
| Powertype: | Steam |
| Designer: | Nigel Gresley |
| Builddate: | 1913–1919 |
| Totalproduction: | 20 |
| Whytetype: | 2-8-0 |
| Uicclass: | 1′D h2 |
| Leadingdiameter: | 3feet |
| Coupleddiameter: | 4feet |
| Length: | 60feet |
| Locoweight: | 76.2LT78.65LT |
| Fueltype: | Coal |
| Firearea: | 27square feet |
| Diameterinside: | 5feet |
| Boilerpressure: | 1802NaN2 |
| Totalsurface: | 2084square feet |
| Fireboxarea: | 162square feet |
| Superheatertype: | 24 |
| Superheaterarea: | 570square feet |
| Cylindercount: | Two, outside |
| Cylindersize: | 21x |
| Valvegear: | Walschaerts |
| Valvetype: | 100NaN0 piston valves |
| Tractiveeffort: | 337352NaN2 |
| Powerclass: | 8F |
| Axleloadclass: | Route availability 6 |
| Nicknames: | Tangos |
| Withdrawndate: | 1947–1952 |
| Disposition: | All scrapped |
The Great Northern Railway (GNR) Class O1 was a class of two-cylinder 2-8-0 steam locomotive designed by Nigel Gresley for heavy freight work and built by the GNR between 1913 and 1919.
Gresley designed the O1 2-8-0 for the heavy coal trains on the mainline from Grantham to London, ordering five examples 1913, which were completed at Doncaster in 1914. A further fifteen were ordered in January 1916, but due to the First World War delays were incurred and construction was transferred to the North British Locomotive Company, who delivered the first ten in April 1918, followed by a further five in October and November 1919.
| Quantity ! | GNR Nos. | LNER Nos. | LNER 1944 Nos. | Notes | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1913–14 | EO 274 | 1411–1413, 1415, 1418 | 5 | 456–460 | 3456–3460 | 3475–3479 | align=left | |||
| 1919 | North British Locomotive Co. (Hyde Park Works) | 22060–22069 | 10 | 462–471 | 3462–3471 | 3480–3489 | align=left | |||
| 1919 | North British Locomotive Co. (Atlas Works) | 22099–22103 | 5 | 472–476 | 3472–3476 | 3490–3494 | align=left |
The class was re-designated O3 by the London and North Eastern Railway in 1944.
Seventeen examples survived into British Railways ownership in 1948, but all had been withdrawn by 1952.
| Quantity in service at start of year | Quantity withdrawn | Locomotive numbers | Notes | ||||
| 1947 | 20 | 3 | align=left | 3487, 3490, 3492 | align=left | ||
| 1948 | 17 | 2 | align=left | 3489/94 | align=left | ||
| 1949 | 15 | 0 | align=left | – | align=left | ||
| 1950 | 15 | 1 | align=left | 63491 | align=left | ||
| 1951 | 14 | 10 | align=left | 63475/77–81/83/85–86/93 | align=left | ||
| 1952 | 4 | 4 | align=left | 63476/82/84/88 | align=left |