Abstract: A gearbox comprising: an input shaft (9) having first and second helical input gears (1, 2) of opposite hand fixed axially relative to each other and axially moveable in tandem; an output shaft (10); first and second lay shafts (7, 8) offset from the axis of the input shaft (9, 10) and configured to engage with the input and output shafts (9, 10) for transmitting rotational movement from the input shaft (9) to the output shaft (10), each lay shaft (7, 8) comprising an input gear (3, 4) such that the first lay shaft (7) engages with the first input gear (1) but not the second input gear (2) and the second lay shaft (8) engages with the second input gear (2) but not the first input gear (1), and two or more output gears (26) rotatably mounted on, and selectively engageable with, the output shaft (10), the output gears being in continuous mesh with corresponding output gears (5, 6) on the first and second lay shafts (7, 8), wherein the gearbox is configured such that an imbalance in load sharing between the inpu