Downhole device delivery and associated drive transfer system and method of delivering a device down a hole

A downhole device delivery and drive transfer system 10 comprises a sub 12 which is arranged to attach to a drill string 14 and a tool 16 which is configured to enable it to travel through the drill string 14 and releasably couple to the sub 12. The sub 12 and the tool 16 are arranged so that when they are releasably coupled to each other torque imparted to the drill string is transferred by the sub 12 to the tool 16. The tool 16 is arranged to carry one or more devices for performing one or more downhole functions such as core drilling, hole reaming or wedge placement for directional drilling. The system 10 also has a guide mechanism 24 that operates between the sub 12 and the tool 16 to guide the tool 16 to a known rotational orientation relative to the sub 12 as the tool 16 travels into the sub 12. A fluid control system controls the flow of fluid through the tool through a downhole outlet and and a plurality of ports intermediate opposite ends of the tool.