The Justice Ministry said today the decision was made after evidence pointed to "reasonable suspicion" of individuals involved in the case.
It said Netanyahu is not among the suspects in the case, according to "findings" so far.
Suspicions of impropriety were heightened when former Defense Minister Moshe Yaalon said he was sidelined on the purchase plans which went forward after he was replaced last year.
Police have been questioning Netanyahu for several weeks over separate corruption allegations the prime minister has dismissed as "baseless.