North of the Static Test Stand in Marshall Space Flight Center's East Test Area is the gantry crane. Mounted on rails, it can move into position to facilitate installation of a stage in the test stand (e.g., as in MSFC-6518198 or MSFC-6520960) or it can move entirely out of the way so that it is clear of the exhaust plume when actually performing a test firing (as in MSFC-6413599; note the gantry crane at the far right).

This diagram illustrates the crane and its rail system.

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From p. 33 (p. 32 in the PDF) of Handling, Transporting and Erection Instructions: Saturn S-1 Stage, SA-1 (EP-141)
Scan and clean-up by heroicrelics.