A drive transmission apparatus comprising a dog clutch comprising: a dog gear assembly, and a dog ring, wherein the dog gear assembly and the dog ring are configured for rotation about a rotational axis, and for relative axial adjustment between an engaged condition in which torque can be transmitted between the dog gear assembly and the dog ring, and a disengaged condition in which torque cannot be transmitted, wherein the dog gear assembly includes: a dog gear, a retractable dog assembly configured for movement relative to the dog gear between an extended position and a retracted position, and a control element that controls movement of the retractable dog assembly, wherein the dog ring comprises a plurality of first dogs, and the dog gear assembly comprises a plurality of second dogs, wherein the second dogs are configured to engage the first dogs in the engaged condition to transmit torque between the dog ring and the dog gear assembly, and are disengaged from the first dogs in the disengaged condition, said second dogs including a plurality of fixed dogs that are mounted on the dog gear, and a plurality of retractable dogs that comprise the retractable dog assembly, characterised in that each retractable dog has a torque drive face that is configured to transmit torque to the dog ring when engaged with a first dog, and a cam face that is configured to drive movement of the retractable dog assembly towards the retracted position when engaged with a first dog, whereby relative rotation between the dog ring and the dog gear assembly causes the engaged first dog to slide over the cam face of the engaged retractable dog, driving movement of the retractable dog assembly towards the retracted position against the force of the control element. a dog gear assembly, and a dog ring, wherein the dog gear assembly and the dog ring are configured for rotation about a rotational axis, and for relative axial adjustment between an engaged condition in which torque can be transmitted between the dog gear assembly and the dog ring, and a disengaged condition in which torque cannot be transmitted, wherein the dog gear assembly includes: a dog gear, a retractable dog assembly configured for movement relative to the dog gear between an extended position and a retracted position, and a control element that controls movement of the retractable dog assembly, wherein the dog ring comprises a plurality of first dogs, and the dog gear assembly comprises a plurality of second dogs, wherein the second dogs are configured to engage the first dogs in the engaged condition to transmit torque between the dog ring and the dog gear assembly, and are disengaged from the first dogs in the disengaged condition, said second dogs including a plurality of fixed dogs that are mounted on the dog gear, and a plurality of retractable dogs that comprise the retractable dog assembly, characterised in that each retractable dog has a torque drive face that is configured to transmit torque to the dog ring when engaged with a first dog, and a cam face that is configured to drive movement of the retractable dog assembly towards the retracted position when engaged with a first dog, whereby relative rotation between the dog ring and the dog gear assembly causes the engaged first dog to slide over the cam face of the engaged retractable dog, driving movement of the retractable dog assembly towards the retracted position against the force of the control element. a dog gear, a retractable dog assembly configured for movement relative to the dog gear between an extended position and a retracted position, and a control element that controls movement of the retractable dog assembly, wherein the dog ring comprises a plurality of first dogs, and the dog gear assembly comprises a plurality of second dogs, wherein the second dogs are configured to engage the first dogs in the engaged condition to transmit torque between the dog ring and the dog gear assembly, and are disengaged from the first dogs in the disengaged condition, said second dogs including a plurality of fixed dogs that are mounted on the dog gear, and a plurality of retractable dogs that comprise the retractable dog assembly, characterised in that each retractable dog has a torque drive face that is configured to transmit torque to the dog ring when engaged with a first dog, and a cam face that is configured to drive movement of the retractable dog assembly towards the retracted position when engaged with a first dog, whereby relative rotation between the dog ring and the dog gear assembly causes the engaged first dog to slide over the cam face of the engaged retractable dog, driving movement of the retractable dog assembly towards the retracted position against the force of the control element.