During 1869 military exercises in Dover included drawing a battery of guns from the railway station up to the castle, a high, steep hill. As a result of this steam sapper number 2 was purchased in 1871. This was a lighter and more powerful engine than number one. The engine was rated 7 nhp (compared to 6), used spur gears for the drive (compared to chain) and used a differential drive on the rear axle to avoid the need to disconnect one wheel which the earlier locomotive had required. On test it drew up the 1 in 11 gradient of Star Hill, Rochester.