Safety of personnel in the vicinity of a gas-insulated transmission line (GIL) is very high because the solid metallic enclosure provides reliable protection. The GIL can be laid aboveground on structures, in a tunnel, or directly buried into the soil like an oil or gas pipeline. The most economical and fastest method of laying cross country is the directly buried GIL. For the purpose of commissioning, comprehensive electrical and mechanical tests are necessary to verify the properties of the directly buried GIL. To check whether arcing due to internal faults causes burn-through of the enclosure, an internal-arcing test was performed on the GIL prototype. Going underground for directly buried systems, the situation regarding corrosion changes and a corrosion protection is required. Two basic methods are used: a passive corrosion protection and an active corrosion protection. Active corrosion protection can be easily installed along with the electrical transmission system, with no interferences between electrical transmission and the corrosion protection voltage potential.