Operation Tracer was a top-secret WWII mission in which six men were to be buried alive inside the Rock of Gibraltar so they could monitor enemy movements after the Rock’s capture. There was no way out and anyone who died within the chamber would have to be embalmed and cemented into the floor. The men understood that they would remain sealed within the facility for about a year, although it could be much longer. Provisions for a seven-year stay had been assembled in the complex. The entirety of the main chamber had been plastered and its floor covered in cork tiles, both methods to reduce sound transmission. The entrance passage had loose soil, to facilitate burials if needed.