From Halopedia, the Halo wiki
Fetching is a human industry that arose following the Human-Covenant War. With the great amount of derelict warships floating in space, the UNSC reasoned that it could recover a good amount of working Shaw-Fujikawa Translight Engines. Thus, companies such as Warner & Ives began contracting "fetchers" to prospect battlefield wreckages and recover usable drives. Fetchers often used magnetic vices to grip metal objects. Oliver Birch was a fetcher. Steve served as a contract handler for Birch and other fetchers.
It is considered important to have two ships available when fetching, primarily because a fetcher often has to enter dense debris fields, something that is not possible for most reasonably priced slipspace-capable ships. For example, Oliver Birch had a small tug, the Galileo's Worst Enemy, for fetching runs of about four to five thousand kilometers, while using the slipspace-capable CAA Butterworth as a base of operations and for interstellar journeys.
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