| NZR WAB class | |
| Powertype: | Steam |
| Builddate: | 1939 |
| Builder: | NZR Addington Workshops, Christchurch (1+1) NZR Hillside Workshops, Dunedin (12+8) A & G Price Limited, Thames (3+5) |
| Locoweight: | 74LT[1] |
| Whytetype: | 4-6-4T |
| Firstrundate: | 1918 - 1926 |
| Disposition: | Scrapped, three preserved |
| Numinclass: | 30 (16 WAB+14 WS) |
| Weightondrivers: | 41.85LT |
| Wheelbase: | 33feet |
| Boilerpressure: | 2000NaN0 |
| Currentowner: | Feilding and District Steam Rail Society (1) |
| Wheeldiameter: | 543NaN3 |
| Cylindercount: | Two |
| Cylindersize: | 17x |
| Poweroutput: | 1000bhp |
| Tractiveeffort: | 22250abbr=onNaNabbr=on |
| Maxspeed: | 60mph |
| Retiredate: | 1967 - 1972 |
| Scrapdate: | 1969 - 1972 |
| Locale: | All of New Zealand |
| Fleetnumbers: | 687 - 798 |
| Length: | 44feet |
| Fueltype: | Coal |
| Watercap: | 1700impgal |
| Fuelcap: | 3LT |
| Firearea: | 33square feet |
| Totalsurface: | 1050square feet |
| Superheaterarea: | 183square feet |
The NZR WAB class locomotives were steam locomotives designed, built and used by New Zealand Railways Department (NZR). Their wheel arrangement is described by the Whyte notation 4-6-4T. The locomotives were designed by NZR chief draughtsman S.H. Jenkinson as tank versions of the AB class 4-6-2 Pacific locomotive. Initially, the locomotives were separated into two classes, designated WAB for mainline work and WS for suburban work.
The remaining locomotives were kept in service until the last days of steam, operating short-haul mainline freight services and fast suburban services, particularly in Auckland. WAB 794 was sold to the Ohai Railway Board in Southland for running heavy coal trains. The locomotives were progressively withdrawn in the 1960s.
The first locomotives, WS 686 and WAB 687, were built from the boilers, frames and engine units initially destined for AB 666 and AB 667. These entered service in 1917, WS 686 in Wellington and WAB 687 at Taumarunui in the central North Island. Fourteen WS class locomotives were built between 1917 and 1925: one at Addington workshops (686), five at A & G Price Ltd, Thames (799-803) and eight at Hillside workshops, Dunedin (764-771). All the WS class were converted to WAB in 1932-4. Sixteen WAB class were built between 1918 and 1926: one at Addington (687), 12 at Hillside (786-795) and three at A&G Price (796-798). In July 1922[2] the class was introduced on Auckland (until 1930 at Waitematā) to Papakura suburban services.[3] Between 1947[4] and 1957, 11 WAB class were converted to AB class,[5] following Wellington electrification,[6] to reduce axle loads, for use on lighter lines.[7]
Only three examples of the class remain, with two in their original form as WABs: