Complex sentence: Most of them went to South West Africa (Namibia), where fifty-five of them would be in operation until strengthening of the track and the introduction of diesel traction made them available to be employed elsewhere.
Split into simpler sentences: Most of them went to South West Africa (Namibia), where fifty-five of them would be in operation. They remained in that territory until strengthening of the track and the introduction of diesel traction made them available to be employed elsewhere.