By May 1985, three months behind schedule, the review board narrowed the tenders down to two contenders in each group: IKL/HDW and Kockums for the submarine, Rockwell and Signaal for the combat system. The "Walrus" and Type 2400 submarine designs were considered to be too expensive to manufacture because of inefficient building practices, while the combat data system tenders had been narrowed down by unjustified development risk in the Plessey and Krupp/Ferranti proposals, and the dual problems in the Sintra Alcatel tender of excessive power usage and incompatibility with the proposed American weapons system. On 9 May, the Australian cabinet approved the selections for the funded studies and decided that six submarines would be built, with the option for two more, all in Australia.