2.19 MOD restricted the competition to UK based companies, although UK based subsidiaries of foreign companies were eligible to participate, because the project was exempt on national security grounds from European Union procurement requirements. MOD received 47 responses to its advertisement for interest in December 1996 from which it selected 33 companies to pre-qualify for the following stages of the procurement through responding to a Preliminary Information Memorandum. Eight consortia responded, and MOD invited a long list of six consortia to submit outline proposals, which did not have to be costed.