Despite the success of his class A, Maznicek wanted something faster for the express trains, whose loadings and schedules, even in the mid-1840s, were becoming more and more demanding. The result, fully in accordance with the wisdom of the day, was this slender long-boiler, of which the patent-holders themselves delivered thirty examples between 1846 and 1848. The inside frames represented a rare exception to an unspoken RSR rule of the 19th century. This was probably due to the difficulty of supporting the firebox with the rear driving wheels in the way, had outside frames been used. The pulling power of the Bs was more than enough for quite a few years but by the late 1850s they were more or less outclassed, and so were displaced by the A1s of 1855 and finally succumbed, like so many others, to the "Allegrettos". The last two were withdrawn from Tupfdu Rulauriku in 1867.

The engine shown, no. 72, ran for a short time in 1854 with a six-wheeled tender.

Text and graphics © Norman Clubb 2012