The armed forces have advertised in the Guardian for a long time, as it is generally the best newspaper for sourcing graduates.
Interestingly, 'Lord' Ashcroft's effort this Parliamentary session seems to have amounted to trying to get the Govt to move all civil service advertising away from the Guardian. Coincidentally, this campaign started round about the same time as the paper published more research into his financial affairs and tax evasion.
Bit unfair, mind, since the Guardian's espousal of the Lib dems probably helped the Tories into power...