Good question - I have no idea. But if I google 'gas-filled tube ethernet', I get a number of hits like http://en.tdk.eu/blob/174150/download/5/smd-surge-arresters-... and http://www.first-electronic.com/uploadfile/2010989552637708.... which suggest that these products are sold for networking purposes to prevent surges. Since this is in a military context, I would hazard a guess that this may be some sort of standard hardening requirement to try to protect the datacenter against lightning strikes, EMPs (such as from nuclear strikes), and general accidents. This may sound paranoid, but then again, so do Faraday cages, and it is the military - it's their job.