In outline they resembled the Clayton Type 1 (Class 17) locomotives, having a cab which was nearly central with bonnets at each end, but with a fixed 0-6-0 wheel configuration rather than bogies as seen on all the other Type 1 classes. The locomotives were powered by a Paxman 6 cylinder Ventura 6YJXL engine producing 650bhp (484kW), connected to a Voith L217U hydraulic transmission and Hunslet gearbox. The axles were connected by coupling rods and driven by a jackshaft located under the cab, between the second and third axles.
The last locomotive built, D9555, is notable as the final locomotive to be built at Swindon Works, in 1965. Today the locomotive is privately-owned and operates on the Dean Forest Railway, Gloucestershire, its original route.
Unusually, D9504 was leased in 2005 from its preservation group and found itself in revenue-earning service on the newest mainline in the UK – High Speed 1 (known as the Channel Tunnel Rail Link during construction) – mainly in marshalling and stabling the 450 metre, 22-wagon concrete-pumping train on the final stretch to St.Pancras Station.
| Key: | Preserved | Scrapped | Exported |
|---|
| Depot codes | |
|---|---|
| Code | Depot |
| 50B | Hull Dairycoates |
| CF | Cardiff Canton |
| LE | Swansea Landore |
| Loco | Final depot | Industrial career | Dates | Disposal |
|---|---|---|---|---|
| D9500 | CF | NCB Ashington | 11/69—? | Preserved by Heritage Shunters Trust |
| D9501 | CF | - | - | Scrapped at C F Booth, Rotherham (6/68) |
| D9502 | CF | NCB Ashington | 07/69—? | Preserved by Heritage Shunters Trust |
| D9503 | 50B | BSC Harlaxton BSC Corby | 11/68—07/74 07/74—09/80 | Scrapped at BSC Corby (09/80) |
| D9504 | 50B | NCB Philadelphia NCB Bolden NCB Burradon NCB Ashington | 11/68—08/73 08/73—12/74 01/75—09/81 09/81—? | Preserved at High Speed 1 Swanscombe |
| D9505 | 50B | APCM Hope, Derbyshire | 09/68—05/75 | Exported to Bruges, Belgium (05/75) |
| D9506 | CF | - | - | Scrapped at Arnott Young Ltd., Parkgate (05/68) |
| D9507 | 50B | BSC Corby | 11/68—09/82 | Scrapped at BSC Corby (09/82) |
| D9508 | LE | NCB Ashington | 03/69—01/84 | Scrapped at D. Short, North Shields (01/84) |
| D9509 | CF | - | - | Scrapped at G Cohen Ltd., Kettering (11/70) |
| D9510 | 50B | BSC Buckmaster BSC Corby | 12/68—06/72 06/72—08/82 | Scrapped at BSC Corby (08/82) |
| D9511 | 50B | NCB Ashington | 11/68—07/79 | Scrapped at NCB Ashington (07/79) |
| D9512 | 50B | BSC Buckmaster BSC Corby | 12/68—09/72 09/72—02/82 | Scrapped at BSC Corby (02/82) |
| D9513 | CF | Arnott Young Ltd., Parkgate NCB Crigglestone NCB Astley NCB Ashington | 07/68—11/68 11/68—09/69 09/69—10/73 01/74—? | Preserved at Embsay & Bolton Abbey Steam Railway |
| D9514 | CF | NCB Ashington | 07/69—12/85 | Scrapped at NCB Ashington (12/85) |
| D9515 | 50B | BSC Buckmaster BSC Corby Hunslet Ltd | 11/68—09/72 09/72—12/81 12/81—07/82 | Exported to Charmartin, Madrid, Spain (07/82) |
| D9516 | 50B | BSC Corby | 11/68—10/81 | Preserved at Nene Valley Railway |
| D9517 | CF | NCB Ashington | 11/69—01/84 | Scrapped at D. Short, North Shields (01/84) |
| D9518 | CF | NCB Ashington | 06/69—??/87 | Preserved at Nene Valley Railway |
| D9519 | CF | - | - | Scrapped at G Cohen Ltd., Kettering (11/70) |
| D9520 | 50B | BSC Corby | 12/68—03/81 | Preserved at Nene Valley Railway |
| D9521 | LE | NCB Ashington | 03/70—11/84 | Preserved at Vale of Glamorgan Railway |
| D9522 | CF | - | - | Scrapped at Arnott Young Ltd., Parkgate (05/68) |
| D9523 | 50B | BSC Corby | 12/68—10/81 | Preserved at Nene Valley Railway |
| D9524 | LE | BP Grangemouth | 07/70—9/81 | Preserved at Bo'ness and Kinneil Railway |
| D9525 | 50B | NCB Philadelphia NCB Ashington | 11/68—03/75 03/75—10/87 | Preserved by Heritage Shunters Trust |
| D9526 | CF | APCM Westbury | 01/70—4/80 | Preserved at West Somerset Railway |
| D9527 | CF | NCB Ashington | 07/69—01/84 | Scrapped at D. Short, North Shields (01/84) |
| D9528 | CF | NCB Ashington | 03/69—12/81 | Scrapped at D. Short, North Shields (12/81) |
| D9529 | 50B | BSC Buckmaster BSC Corby (as No. 61) | 08/68—9/72 09/72—03/81 | Preserved - on hire to High Speed 1 construction project |
| D9530 | CF | Gulf Oil Co.Ltd., Waterston NCB Mardy NCB Tower Colliery | 09/69—10/75 10/75—08/82 08/82 | Scrapped at NCB Tower Colliery (08/82) |
| D9531 | CF | Arnott Young Ltd., Parkgate NCB Crigglestone NCB Burradon NCB Ashington | 07/68—11/68 11/68—10/73 10/73—04/74 04/74—? | Preserved at East Lancashire Railway |
| D9532 | 50B | BSC Corby | 11/68—02/82 | Scrapped at BSC Corby (02/82) |
| D9533 | 50B | BSC Corby | 12/68—09/82 | Scrapped at BSC Corby (09/82) |
| D9534 | 50B | APCM Hope, Derbyshire | 10/68—05/75 | Exported to Bruges, Belgium (05/75) |
| D9535 | CF | NCB Burradon NCB Backworth NCB Ashington | 11/70 — 01/76 01/76—09/80 09/80 — 01/84 | Scrapped at NCB Ashington (01/84) |
| D9536 | LE | NCB Ashington | 03/70—12/85 | Scrapped at NCB Ashington (12/85) |
| D9537 | 50B | BSC Corby | 11/68—11/82 | Preserved at private location |
| D9538 | LE | Shell-Mex & BP Ltd., Shellhaven BSC Ebbw Vale BSC Corby | 04/70—2/71 02/71—04/76 04/76—9/82 | Scrapped at BSC Corby (09/82) |
| D9539 | 50B | BSC Corby | 10/68—02/83 | Preserved at Ribble Steam Railway |
| D9540 | 50B | NCB Philadelphia NCB Burradon NCB Ashington | 11/68—11/71 11/71—06/72 06/72—01/84 | Scrapped at D. Short, North Shields (01/84) |
| D9541 | 50B | BSC Harlaxton BSC Corby | 11/68—08/74 08/74-08/82 | Scrapped at BSC Corby (08/82) |
| D9542 | 50B | BSC Corby | 12/68—08/82 | Scrapped at BSC Corby (08/82) |
| D9543 | 50B | - | - | Scrapped at C F Booth, Rotherham (11/68) |
| D9544 | 50B | BSC Corby | 11/68—09/80 | Scrapped at BSC Corby (09/80) |
| D9545 | 50B | NCB Ashington | 11/68—07/79 | Scrapped by D. Short, North Shields (07/79) |
| D9546 | 50B | - | - | Scrapped at C F Booth, Rotherham (11/68) |
| D9547 | 50B | BSC Corby | 12/68—08/82 | Scrapped at BSC Corby (08/82) |
| D9548 | 50B | BSC Harlaxton BSC Corby Hunslet Ltd | 11/68—08/74 08/74—11/80 11/80 — 07/82 | Exported to Charmartin, Madrid, Spain (07/82) |
| D9549 | 50B | BSC Corby Hunslet Ltd | 11/68—11/81 11/81—7/82 | Exported to Charmartin, Madrid, Spain (07/82) |
| D9550 | 50B | - | - | Scrapped at C F Booth, Rotherham (11/68) |
| D9551 | 50B | BSC Corby | 12/68—06/81 | Preserved at Royal Deeside Railway |
| D9552 | 50B | BSC Buckmaster BSC Corby | 09/68—06/72 06/72—09/80 | Scrapped at BSC Corby (09/80) |
| D9553 | 50B | BSC Corby | 11/68—? | Preserved at Gloucestershire Warwickshire Railway |
| D9554 | 50B | BSC Corby | 11/68—08/82 | Scrapped at BSC Corby (08/82) |
| D9555 | LE | NCB Burradon NCB Ashington | 03/70 — 02/75 02/76—??/87 | Preserved at Dean Forest Railway |