Holy War is a preserved narrow gauge steam locomotive built in 1902, based at the Bala Lake Railway in North Wales.

[4] It spent its whole working life in the quarry, alongside other Hunslet engines including Dolbadarn, George B, Maid Marian, Red Damsel, Wild Aster, Alice and Irish Mail.

[5] By 1967 Holy War was the last steam locomotive in operation in a North Wales slate quarry,[2] being withdrawn in November that year.

[5] After being used in Buckinghamshire it was purchased by Rev Alan Cliff and returned to Wales in 1975, going to the Bala Lake Railway.

Holy War appears in the children's book "Jack the Station Cat and the Great Little Trains Robbery".